2005 'hoe - Rattle ONLY at 1300RPM's and ONLY in gear

[MikeTheApeman]

I've searched and searched, no clue what this might be.
It's a 2005 Tahoe, bone stock except a drop in AFE Filter and Airraid Jr. Kit.
5.3L engine, AWD, just flipped 60k miles.
Over the last two weeks, I have noticed a rattle that sounds almost like a loose heat shield coming from under the truck. I had the mrs roll back and forth in the driveway while I listened, hood was up, rattle is most def coming from underneath. It ONLY rattles in gear at 1300RPM's. I couldn't get it to duplicate in neutral or park, only in gear.
That last fact is leading me to believe that it's drive train related, read some things that said it could be u-joints. Some posts said it was the cat going bad.

Anyone experience this sound / gremlin? What was your fix?

 

[Boomer73]

I had a loose baffle in the muffler that rattled like that and strangely only when in gear, but that was at the back, not at the front.

-B

 

[ScottyBoy]

I had a similar issue on mine. It turned out to be the exhaust heat shield thats mounted on the passenger side of the transmission. The bolts had somehow gotten a little loose. Not sayin thats your problem though. You'll have to get under your truck and just keep looking around.

 

[MikeTheApeman]

When I was outside the truck, it sure sounded like it was coming from inside the muffler, but there was no visible damage (i.e. cracks, rust, holes). But the baffles are internal, right? I guess if one did come loose I wouldn't be able to see it. I'll check the heat shields again tonight. Was gonna go get a new muffler in a few weeks anyway (Needs me some growl. ) but wanted to make sure this isn't a tell-tale sign that something big's gonna fail before I go spending money on an exhaust.
Only reason I mentioned the hood was up and it's def under the truck is I read a few things that said it was something loose in the engine compartment, so I wanted to get that outta the way.

 

[bluekon]

I had a similar issue on mine. It turned out to be the exhaust heat shield thats mounted on the passenger side of the transmission. The bolts had somehow gotten a little loose. Not sayin thats your problem though. You'll have to get under your truck and just keep looking around.

i had the same problem just got under there and bent it away an inch or so problem solved

 

[dwmmatt23]

im trying to find the culprit right now what sounds to be the exact same thing. bugging the heck out of me.

 

[ScottL4619]

I had the same problem and it was my heat shield above the muffler. They spot welded it and it came back in 3 months. They then put some sort of clamp on and it's been good since.

The reason you only hear it when in gear is because the truck has a different vibration frequency when in gear than it does in neutral. FYI - this is not scientific, but seems to make sense to me.

 

[Boomer73]

When I was outside the truck, it sure sounded like it was coming from inside the muffler, but there was no visible damage (i.e. cracks, rust, holes). But the baffles are internal, right?

Yes, baffles are internal, thats what muffles the sound of the exhaust. This isn't the first, or second, or third, or fourth, or...ahem... GMT800 I've heard of with loose muffler baffles. What's odd is I've never heard about it in an 03 or 04 only 05 and 06. Did they change the muffler or switch suppliers or something then?

The reason you only hear it when in gear is because the truck has a different vibration frequency when in gear ...

I believe this is true.

 

[BOSS]

My guess is heat shield, had the same rattle..x3 on the in gear thing, different vibration level produces different harmonic

B

 

[MikeTheApeman]

Sure enough, just crawled under the truck and the heat shield on the muffler is cracked at the back left corner. Bent it away for now and seems to have done it, but I'm just gonna have to get a new exhaust now cause...ya know...bending metal is just a band aid.

 

[Tomg49]

Sure enough, just crawled under the truck and the heat shield on the muffler is cracked at the back left corner. Bent it away for now and seems to have done it, but I'm just gonna have to get a new exhaust now cause...ya know...bending metal is just a band aid.

How lucky can one be to find this forum , I been having this same rattle in my 2005 Tahoe Z71 for about three weeks now..At first it sounded as if it was in the rear of the truck. Then after opening windows, it moved to the center. I crawled under there, did not spend a lot of time, but I notice the center strap band that's around the muffler was rusted into and just hanging. I thought how easy of fix was that,,Well as it turned out, that was not the rattle..Its just like someone said, right at 800 -1200 RPMs when taking off..For the life of me, I have no idea if that missing strap in the center of the muffler is the reason or not. I have to go to Indy, Thursday , that's a 200 miler, so I hope nothing falls off..Then I'll be heading to the Chevy Dealer to takes care of my truck. I let you guys know what was wrong,,I just hope I don't need a new exhaust system, they are about 450.00 if you buy the best Flow Master.....La8er..

 

[SLCHOE]

Get under the truck and smack the catalytic converters with the side of your fist. If it rattles, the substrate inside has come apart. You will need a new cat (or 2) and need to find the source of the rich condition which caused it in the first place.

 

[Tomg49]

OK fellows , I did a little work on my 2005 Z71 Tahoe yesterday. that had a rattle around the 800 to 1300 RPM's ... Found out that 2 of 3 bands were missing off the heat shield off the muffler. These bands were just like a metal band that many crates would be band with..1/2 wide and 24 inches long..
So I headed to my nearest Napa Auto Parts. They have stainless hose clamps that worked great. They were about 30 inch's long..So after wrapping one around the shield and muffler, I needed to cut off and 5 inches of the band,..While working on the two missing, I used a cut off tool to remove the last of the old, and replaced it as well...
The Napa Auto Part # BK 705-1154...I think they are about $4.00 each, or a box of 5 just under 20 bucks.....Hope this info helps out , I know these rattle drove me crazy until found this forum and this thread, where to even start looking for this rattle....