Billet Grille Noise - resonant whirring sound at 55+mph

[Colby82]

Billet Grille Noise - resonant whirring sound at 55+mph ***UPDATE: FIXED***

I installed the billet grille Friday and now I have a resonant whirring noise right at 35mph and anything over 55mph. It changes or stops when I get a different draft behind/beside somebody or if it's raining. I Googled and found some fixes that talked about using black silicone on the backside tips of the grille fins to bond them to the grille shell. Others tried strapping the stock grille shell to the back of the billet grille. This was a cutout billet grille.

Anybody ever had this problem?

UPDATE: Fixed! After multiple attempts to ditch the noise, I was able to install additional vertical support bars to resolve the problem. See post 17 for details.

 

[Colby82]

I pulled the grille shell off today and added black silicone. I put a small bead from the end of each fin to the grille shell on the rear side. It can't be seen from the front since it's dark behind the grille. It pretty much eliminated the noise at 35mph but only changed it to a higher pitch noise at 55+mph.

I'm thinking about trying some metal mesh behind the billet pieces next. I'm hoping it'll break up the wind enough to stop the noise and be undetectable if it's painted a flat or satin black.

This is insane

 

[Anonymous]

Resonant wind noise can be a real *****. Sounds like its an insert, so the first thing would be to make sure the ends are firmly attached to the grille surround. If it still gives you issues, you need to change the resonant frequency of the bars themselves. Pictures would be a help here.

 

[zieglerj-pdm-specialist]

I hope this helps

Resonant wind noise can be a real *****. Sounds like its an insert, so the first thing would be to make sure the ends are firmly attached to the grille surround. If it still gives you issues, you need to change the resonant frequency of the bars themselves. Pictures would be a help here.

I agree resonance is a ***** because the grille maybe vibrating but unfortunately it not and the whirr is audible. Have you tried adding more mounts on the grille to stiffen it to eliminate the whir sounds. Are you using the same grill outside lining and just cut the original OEM Grill out and mounted the Billet grille to the OEM outside shell. That is what I did and I didn't have any different noise come through. Was this grille one big place that replaces the whole unit or did you cut out the GMC Grille and mount the Billet to the outer shell. Take Care

 

[Anonymous]

I agree resonance is a ***** because the grille maybe vibrating but unfortunately it not and the whirr is audible. Have you tried adding more mounts on the grille to stiffen it to eliminate the whir sounds. Are you using the same grill outside lining and just cut the original OEM Grill out and mounted the Billet grille to the OEM outside shell. That is what I did and I didn't have any different noise come through. Was this grille one big place that replaces the whole unit or did you cut out the GMC Grille and mount the Billet to the outer shell. Take Care

Yes, the grill can create a sonic resonator and whistle effect, but you can't solve that until you have it rigidly mounted. After that, either the bars themselves could vibrate or they could whistle. Adding silicone or rubber in the right place to change either the vibration frequency of the grille or brake up the air flow is then required. That's why I asked for pictures.

 

[Colby82]

Resonant wind noise can be a real *****. Sounds like its an insert, so the first thing would be to make sure the ends are firmly attached to the grille surround. If it still gives you issues, you need to change the resonant frequency of the bars themselves. Pictures would be a help here.

This is a cutout billet grille. You take the grille shell off, cut the gray plastic insert out of the grille opening and bolt a billet insert in it's place. I'm not sure how pictures of that would help? I'm also not sure of what you mean by changing the resonant frequency of the bars themselves....I guess if I knew how to do that then I wouldn't have the noise now.

I agree resonance is a ***** because the grille maybe vibrating but unfortunately it not and the whirr is audible. Have you tried adding more mounts on the grille to stiffen it to eliminate the whir sounds. Are you using the same grill outside lining and just cut the original OEM Grill out and mounted the Billet grille to the OEM outside shell. That is what I did and I didn't have any different noise come through. Was this grille one big place that replaces the whole unit or did you cut out the GMC Grille and mount the Billet to the outer shell. Take Care

The grille is tight....it's solidly mounted in the shell. Maybe I should loosen it up because an inaudible rattle would be way better than an audible whirring noise lol. Yes, the stock chrome grille shell is still in place. I only replaced the plastic filler in the opening of the grille with a billet piece.

I have suspicion that the resonant noise is coming from the ends of the horizontal bars. I'm going to try to secure them by mounting a vertical bar or the stock grille insert in behind the billet. The silicone bead that I've already added to the end of each horizontal bar definitely made a difference in the noise, so I think I'm in the right area.
Before:


After cutting out the stock gray piece and bolting in the billet:

 

[Anonymous]

You can change the resonant frequency of something by changing its mass, its stiffness, how it attaches to the world around it, or all three.

Hard to tell by the far away pictures, but that kind of insert usually has vertical bars every few inches and the ends are free. Most materials won't have an audible resonance with both ends fixed over a distance of less then 4-6 inches. If an end is free, then it might. You said siliconing the ends helped. I bet it would improve even more if you used a hard epoxy instead of silicone to attach the ends of the bars to the grille surround. Once we you are sure the grille bars are solid and can't move freely at the ends, that only leaves a sonic resonance or whistling caused by airflow.

Mounting the stock insert or a screen behind the bars can break up flow and stop the whistle, but could also block airflow into the radiator. As whistling can be caused by a sharp trailing edge transition and separation, tapering the trailing edge and smoothing the transition can eliminate the problem. Something as simple as a small tab of stiff clear plastic (don't want anything else vibrating) on the trailing edge of teh bars can break up the separation pattern and eliminate the whistle. Without a wind tunnel, you'll just have to play around until the whistle stops.

 

[Colby82]

You can change the resonant frequency of something by changing its mass, its stiffness, how it attaches to the world around it, or all three.

Hard to tell by the far away pictures, but that kind of insert usually has vertical bars every few inches and the ends are free. Most materials won't have an audible resonance with both ends fixed over a distance of less then 4-6 inches. If an end is free, then it might. You said siliconing the ends helped. I bet it would improve even more if you used a hard epoxy instead of silicone to attach the ends of the bars to the grille surround. Once we you are sure the grille bars are solid and can't move freely at the ends, that only leaves a sonic resonance or whistling caused by airflow.

Mounting the stock insert or a screen behind the bars can break up flow and stop the whistle, but could also block airflow into the radiator. As whistling can be caused by a sharp trailing edge transition and separation, tapering the trailing edge and smoothing the transition can eliminate the problem. Something as simple as a small tab of stiff clear plastic (don't want anything else vibrating) on the trailing edge of teh bars can break up the separation pattern and eliminate the whistle. Without a wind tunnel, you'll just have to play around until the whistle stops.

It has vertical support bars in 3 places I believe...middle and then about 4 inches from each end. I believe the noise is coming from the unsupported ends that extend out from the outside vertical bars. To troubleshoot I strapped some 1/2" CPVC to the outside ends of each grille insert. This also changed the noise....it is now a higher pitch noise at about 60+mph. I think I've identified the right section of the grille making the noise, I just need to find an effective method of securing these horizontal pieces that will prevent them from resonating.

I don't plan on leaving the CPVC, I just wanted to see if the general idea was going to reduce or eliminate the noise before I came up with a more permanent and less visible method. I'll get it silenced, one way or another.

The funny thing is that I installed this same grille on my neighbors Tahoe about 7 years ago....it's quiet. So I know it's possible to have a good looking grille that doesn't make noise.

 

[Colby82]

Progress!

For testing, I cut out some sheet metal pieces and strapped those to the backside of each end of the billet grille inserts and now the noise is GONE

So for a permanent fix, I'll fabricate some sheet metal pieces that are not as wide as these, adhere them to the back of the billet insert with black silicone and then paint the front side of each sheet metal piece flat or satin black. I believe they'll be almost invisible once painted.

Here are the test pieces installed....these are not permanent, only for testing the idea:






I'll post pics of the permanent repair once I get it fab'd up, installed and painted.

---------- Post added at 01:12 PM ---------- Previous post was at 01:09 PM ----------

On a side note, you can't even see the black silicone bead that I added the other day to the back of each grille bar.

I think the new pieces will have minimal effect on the air flow through the grille since they will be about half as wide as these test pieces.

 

[Anonymous]

Looks good. Using half that width shouldn't block too much cooling air. I'd be careful using silicone as adhesive, make sure its rated as an adhesive, not a sealant and is rigid, not flexible. Epoxy might be a better choice, but as long as nothing flies off at 80 mph, all is good.