Mystery noises in engine bay

[Wing Bucket]

I would say both noises are from the alternator. Obvious alternator problem. Replace it and see if the noises both go away. The alternator is right there in the second video.

I just took the belt off, ran it, and shut it off. The whirring/clicking still happened after turning the key off, so I think that rules out the alternator for that particular noise.

 

[SnowDrifter]

Clicking: Sounds like evap purge solenoid. Check is to remove the engine beauty cover - single 8mm bolt. Pull up then forward. It's a vertical thing with a hose and a plug on it just behind the throttle body. Remove the electrical plug. If that is the noise - well... A new one *might* be quieter. But it's not harmful. Just the sound of a valve opening and closing.

Whirring: Confirm it happens w/ BOTH belts off?

- Pop the connection cover off the alt charge wire and just verify the connection is clean and tight.

- One of the noises sounds a bit sad from the alternator. Check the thing for any freeplay both side to side, and in and out. Spin it by hand and feel for any roughness. A bit of noise is normal because of the brushes. But it shouldn't feel rough like there's a bearing going out. Barring that - some just have noisy rectifiers / loud fans. Hell... My last rig had a rather large aftermarket alt and the cooling on the alternator drowned out all engine noise above about 1500 rpm. Just differentiate between functional sounds and bad sounds. Auto parts store should be able to check rectifier electrical noise/ripple and differentiate if there's a bad diode in there.

- Whirring: Mine does this too. Literally, the throttle body whistling at idle. Can rev it slightly, turn on a/c, anything to slightly change the throttle position and the whistling goes away. Checked fuel trims, no vaccuum leak. Just an oddity. If the noise is present w/ belt off, and fuel trims don't indicate a vacuum leak, can leave it alone. Not sure what the cause is, as not all vehicles do it. Maybe some casting seams or tolerance or something.

 

[Wing Bucket]

Clicking: Sounds like evap purge solenoid. Check is to remove the engine beauty cover - single 8mm bolt. Pull up then forward. It's a vertical thing with a hose and a plug on it just behind the throttle body. Remove the electrical plug. If that is the noise - well... A new one *might* be quieter. But it's not harmful. Just the sound of a valve opening and closing.

Whirring: Confirm it happens w/ BOTH belts off?

- Pop the connection cover off the alt charge wire and just verify the connection is clean and tight.

- One of the noises sounds a bit sad from the alternator. Check the thing for any freeplay both side to side, and in and out. Spin it by hand and feel for any roughness. A bit of noise is normal because of the brushes. But it shouldn't feel rough like there's a bearing going out. Barring that - some just have noisy rectifiers / loud fans. Hell... My last rig had a rather large aftermarket alt and the cooling on the alternator drowned out all engine noise above about 1500 rpm. Just differentiate between functional sounds and bad sounds. Auto parts store should be able to check rectifier electrical noise/ripple and differentiate if there's a bad diode in there.

- Whirring: Mine does this too. Literally, the throttle body whistling at idle. Can rev it slightly, turn on a/c, anything to slightly change the throttle position and the whistling goes away. Checked fuel trims, no vaccuum leak. Just an oddity. If the noise is present w/ belt off, and fuel trims don't indicate a vacuum leak, can leave it alone. Not sure what the cause is, as not all vehicles do it. Maybe some casting seams or tolerance or something.

Thanks....

- I removed the electrical plug on the evap purge solenoid. The noise still occurs when the engine is turned off. My best guess at this point is the idle control valve on the side of the throttle body. If I put my hand on it while running and have someone turn the engine off, I can feel it vibrating during the clicking noise. Maybe it’s the plunger/valve returning to home after the key is turned off.

- When testing with the belt off, it was just the main serpentine belt off. The AC belt was still on. The noise is definitely on top by the throttle body.

- The alternator connections are bright. I removed the nuts and reinstalled. The alternator noise has disappeared for now. I’ll see about getting a store or shop to test it.

 

[SnowDrifter]

Thanks....

- I removed the electrical plug on the evap purge solenoid. The noise still occurs when the engine is turned off. My best guess at this point is the idle control valve on the side of the throttle body. If I put my hand on it while running and have someone turn the engine off, I can feel it vibrating during the clicking noise. Maybe it’s the plunger/valve returning to home after the key is turned off.

- When testing with the belt off, it was just the main serpentine belt off. The AC belt was still on. The noise is definitely on top by the throttle body.

- The alternator connections are bright. I removed the nuts and reinstalled. The alternator noise has disappeared for now. I’ll see about getting a store or shop to test it.

Good to hear on the alt

IAC: If it happens reliably on shutdown, give the thing a start, unplug, then turn the engine off. Note if the noise occurs. Someone check me on this as it's been forever since I've diag'd IAC issues: But take the thing off and give it a shake. If the pin rattles around, it's bad.

Whirring/whistling: does it occur with both belts off? Resonances can do funny things.



Whistling: Take the smallest pieces of electrical tape you can use for this, and tape off the holes in the throttle body. The reason for electrical tape and small, is that if it dislodges, it's small enough to burn in combustion without causing other issues. Scotch tape would also work. Just don't use something fibrous like duct tape. Not really any directive in this one, but it'll tell you if that's the source of the whistle. Some aftermarket throttle bodies either exclude these holes, or have a different orientation of them that can quiet it down if it bothers you. Reiterating that fuel trims are a great spot check if you suspect it's a vacuum leak

 

[OR VietVet]

IAC pin rattling bad. May also need to be cleaned at the pintle and at the bore where it mounts at. The pin has a spring on it and can be bad but spring hides the rattle.

 

[iamdub]

Thanks for the tips everyone. Today I took off the fan/clutch. There are still two noises occurring.... If you have any ideas let me know!

There’s a bearing/squeal/chatter noise, which appears to be coming from the alternator. If I press the rubber boot on the output cable, it quiets. Here’s the video:

Possibly worn bearings or brushes or the like in the alternator.

Then there’s the whirring/clicking noise that occurs after the key is turned off. Sounds like it’s coming from behind the throttle body. Here’s a better video:

Thanks

Really sounds like IAC valve returning to its parked position. Probably just slack in its operation from normal age/wear. Both sounds are normal/typical "old GM motor" sounds.

You can remove the TB, then the IAC valve from it to give the IAC pintle and all the passages a good cleaning. But, I don't think this will fix the sound. It's probably not even a problem.

 

[Wing Bucket]

I cleaned the IAC valve. This whole throttle body needs a good cleaning....I’ll add it to the list, haha.

The IAC sound remains, but I’m not overly worried.... My wife drives the Suburban a few days each week so was trying to get ahead of any issues.

Think we’re good for now. Thanks for the input everyone!