97 Tahoe whistling

[Mark97]

Hi!
New forum member here. I hope this is in the right spot.

1997 Tahoe LT 5.7 gas vortec engine.
Last night it just started a really high pitched whistling.
All the time at idle.
When I accelerate, it goes away.
If I'm cruising, it whistles.
It only stops when I accelerate.
No noticeable difference in idle or performance at any speed.

It seems to be loudest on the passenger side of the engine compartment. Other than that, I got nothing.

Any ideas?

Thanks,
Mark

 

[GreyStone]

Hi!
New forum member here. I hope this is in the right spot.

1997 Tahoe LT 5.7 gas vortec engine.
Last night it just started a really high pitched whistling.
All the time at idle.
When I accelerate, it goes away.
If I'm cruising, it whistles.
It only stops when I accelerate.
No noticeable difference in idle or performance at any speed.

It seems to be loudest on the passenger side of the engine compartment. Other than that, I got nothing.

Any ideas?

Thanks,
Mark

check the pcv valve

 

[OR VietVet]

Welcome to the forum from Oregon. Sounds like a vacuum leak but that loud of a leak should cause a running problem. May be a squealing belt, check that. Does it make a difference whether it is in gear when accel or not? An inexpensive mechanic's stethoscope would pin it down quick.



We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.


If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.

 

[Mark97]

The only time the whistle goes away is when I accelerate. No other difference in performance or behavior.

Took off the pcv valve. Cleaned it up. It still rattled freely. Put it back on.


I still have the whistle.

 

[OR VietVet]

Something that loud and distinctive should be easy to pin down.

 

[Danny3737]

Sorry, couldn’t resist

 

[96-2D-Hoe]

Heater control valve solonoid?
Does the AC on or off make a difference?

Gonna have to narrow it down some.

 

[OR VietVet]

Heater control valve solonoid?
Does the AC on or off make a difference?

Gonna have to narrow it down some.

He said the noise was on the passenger side so this could be it. Do the heater and a/c controls work and do the blend doors all move to correct position?

 

[96-2D-Hoe]

There's not a lot of vacuum on the passenger side.

Air intake housing and engine breather are all else I can think might whistle on that side.

 

[PG01]

It whistles because it doesn’t know the words.....

If it goes away when you accelerate.... well you know what to do then....

seriously now, look under passenger side dash, should be some vacuum lines for hvac controls... make sure everything is pushed together... pretty sure that year stil had the clear connector with all diff colored vacuum lines going to it, no?

 

[Mark97]

Sorry, couldn’t resist

Hahahaha!

If it whistled like that I might not mind it as much.

 

[Mark97]

Thanks for the other suggestions. That will give me a few things to check today. I'll let you know what I find later today.

 

[Mark97]

Ok. So this is what I found out today. The whistle only happens when the temperature control is set all the way cold. As soon as I get 4 "clicks" warmer, the whistle goes away. Does not fade out, it just stops.
Happens with the fan on or off. The a/c doesn't matter - on or off it whistles.
Until I go warmer, then it stops. I turn it back cold and the whistle starts again.

Tried every combination of idle, moving, a/c on or off, vent, feet, defrost. It blows hot and cold as appropriate. It just whistles when temperature is set to cold

The pic is the point where the whistling stops.

 

[OR VietVet]

Then that noise could be the controller itself, the connection at the back or the valve under the hood. When it is doing it is the noise inside or out?

The inside controller: https://www.rockauto.com/en/moreinfo.php?pk=85835&cc=1061367&jsn=930

The outside valve: https://www.rockauto.com/en/moreinfo.php?pk=84579&cc=1061367&jsn=982

Heater valve solenoid: https://www.rockauto.com/en/moreinfo.php?pk=1990462&cc=1061367&jsn=985

Or the plethora of connectors at the back of the controller.

 

[96-2D-Hoe]

Check the vacuum line to the heater control valve. There is a soloniod on the firewall and the hose from it should run to the heater control valve which is basically below the air filter. The heater control valve is a black plastic thing with two hoses in and two hoses out that run to the firewall. Link to image

https://www.rockauto.com/en/moreinfo.php?pk=84579&cc=1061356&jsn=753

 

[east302]

Sounds reasonable. The solenoid is energized when the temp dial is set to the “max” detent. That then applies engine vacuum to the heater valve.

The solenoid has a hard vacuum line running from the PCV fitting and across the intake. The soft vacuum line goes from the solenoid to the heater valve.

Sounds like the soft line could be disconnected/broken if it only happens when MAX is selected.

 

[Mark97]

Now that I know it's not an immediate mechanical issue, unfortunately this has gone down a couple slots on my to do list.
Hope to get to it in the next couple days - I will def let you know what I find.