Vibrating/Grinding Noise from top of engine

[cjp24]

I have an 07 Tahoe 5.3L V8, and about a month ago I started noticing a quiet noise when slowing down to a stop, when the engine returned to idle, for a brief second it sounded as though maybe a pulley was bad or AC clutch not disengaging all the way. As two weeks passed, it started lasting longer (up to maybe 10 seconds after stopping and typically causing an RPM fluctuation/idle down as well). Then it started briefly making the noise when turning the car off as well. Then after a week of that, it started making the noise when turning the car on after it was already hot for a brief second. At first it was worse when the car was cool but now it seems to not matter the car temp or outside temp. I removed the AC belt and it still makes the noise, checked pulleys and all feel fine, felt lines and plastic and clips on top of motor and nothing felt loose or rattling. Finally caught the noise on video, will try to figure out how to post. Also able to find that the noise seems to be coming from the top of the engine behind the throttle body. Any one have any ideas?? I'm at a loss and it is driving me crazy

link to sound on YouTube:

 

[wjburken]

I have an 07 Tahoe 5.3L V8, and about a month ago I started noticing a quiet noise when slowing down to a stop, when the engine returned to idle, for a brief second it sounded as though maybe a pulley was bad or AC clutch not disengaging all the way. As two weeks passed, it started lasting longer (up to maybe 10 seconds after stopping and typically causing an RPM fluctuation/idle down as well). Then it started briefly making the noise when turning the car off as well. Then after a week of that, it started making the noise when turning the car on after it was already hot for a brief second. At first it was worse when the car was cool but now it seems to not matter the car temp or outside temp. I removed the AC belt and it still makes the noise, checked pulleys and all feel fine, felt lines and plastic and clips on top of motor and nothing felt loose or rattling. Finally caught the noise on video, will try to figure out how to post. Also able to find that the noise seems to be coming from the top of the engine behind the throttle body. Any one have any ideas?? I'm at a loss and it is driving me crazy

Welcome to the forum from Iowa, CJ.

Most folks find it best to upload videos to YouTube and then share the link here.

Get that video posted and see what the knowledgeable folks here can do for you.

One thing you could do is take the Serpentine belt off and run the engine for a short time to see if the noise remains or goes away. If it remains, you can definitely rule out the belt driven pulleys.

 

[cjp24]

Welcome to the forum from Iowa, CJ.

Most folks find it best to upload videos to YouTube and then share the link here.

Get that video posted and see what the knowledgeable folks here can do for you.

One thing you could do is take the Serpentine belt off and run the engine for a short time to see if the noise remains or goes away. If it remains, you can definitely rule out the belt driven pulleys.

I will try running without belt on tomorrow and see, I have edited the post to include sound from YouTube, thanks!

 

[OR VietVet]

Yes, welcome to the forum from Oregon.

So, you only took one belt off? Why not the other?

You may have a vacuum leak at the back there that is getting progressively worse.

If you can catch it, the best way to find a noise is with a mechanic's stethoscope.

 

[cjp24]

Yes, welcome to the forum from Oregon.

So, you only took one belt off? Why not the other?

You may have a vacuum leak at the back there that is getting progressively worse.

If you can catch it, the best way to find a noise is with a mechanic's stethoscope.

I took both off to check the belts and feel/spin pulleys and then reinstalled the main drive belt and ran it with AC belt off. Simply did not think to run it with both belts off briefly.

 

[swathdiver]

I took both off to check the belts and feel/spin pulleys and then reinstalled the main drive belt and ran it with AC belt off. Simply did not think to run it with both belts off briefly.

Can I infer that after doing this the noise was still there CJ? Listened to the video, it's a new one for me. If repeatable, I would get a long extension or mechanic's stethoscope and touch one end to your ear and the other to various parts of the motor while someone starts and kills the motor until found.

 

[91RS]

Oil level full? Almost sounds a like a lifter bleeding down and makes noise until it gets pumped up with oil/pressure.

 

[Rocket Man]

Any updates?

 

[cjp24]

Just re-stumbled upon this thread while posting a new problem. For someone who may have the same problem now or down the road and stumble upon this thread: I replaced the throttle body due to getting an error code a couple months later while still trying to find this problem. The truck shut off in the middle of the road and threw like 3 different throttle body related error codes. So I cleaned it and continued to occasionally get an error code and still had the odd noise. Replaced the throttle body and haven't received an error code or heard that noise since. Don't know what in the throttle body causes that noise but it obviously was it. Now if only someone can help me with my new problem.

 

[OR VietVet]

Just re-stumbled upon this thread while posting a new problem. For someone who may have the same problem now or down the road and stumble upon this thread: I replaced the throttle body due to getting an error code a couple months later while still trying to find this problem. The truck shut off in the middle of the road and threw like 3 different throttle body related error codes. So I cleaned it and continued to occasionally get an error code and still had the odd noise. Replaced the throttle body and haven't received an error code or heard that noise since. Don't know what in the throttle body causes that noise but it obviously was it. Now if only someone can help me with my new problem.

In a "drive by wire" throttle body, there is a motor that runs the throttle plate instead of the old mechanical throttle cables. The noise you were hearing, was likely the motor and that was causing the problem. Another name for that motor would be the actuator. It is likely encased in a black plastic cover on the side of the throttle body.