Metallic buzz sound when shifting

[gmartin1215]

On my 09 Tahoe with a 6 speed, I am getting a loud metallic buzzing sound when shifting from 2nd to 3rd on hard acceleration (or could be 3rd to 4th, will double-check). The sound does not happen at all gear shifts. What could be the cause of this sound and what could go wrong? Normal driving does not make this sound. Only on hard acceleration.

 

[OR VietVet]

So, I am assuming no CEL? IMO, first thing to do is check trans fluid level and trans fluid condition/color. Then drop pan and see what is in there. Grit/chunks in pan? Maybe @rockola1971 can chime in and give his perspective.

Any recent work done to rig?

 

[gmartin1215]

So, I am assuming no CEL? IMO, first thing to do is check trans fluid level and trans fluid condition/color. Then drop pan and see what is in there. Grit/chunks in pan? Maybe @rockola1971 can chime in and give his perspective.

Any recent work done to rig?

CEL?
Check Engine Light? That was the first thing I checked. Nothing there.
I did drop the pan and changed the fluid and filter about a couple of months ago and only had the fine metal residue that you typically find on the magnet, and the rig has not been driven much. I'll double-check my fluid level. Normal driving is fine, it's just when I do this hard acceleration.

 

[Fless]

I would check all of the heat shields for stability and firmness.

 

[OR VietVet]

I agree with @Fless, likely a heat shield rattle if nothing is obvious about the transmission. Good call.

 

[gmartin1215]

Thanks. But it doesn't make a rattling sound all the time. The only time I hear the sound is when reaching a high RPM (5-6k) then it shifts to the next gear, and not all gear shifts.
I did have the tranny lines changed back in April, but I'll crawl under to check the heat shield.

 

[OR VietVet]

Check the trans lines too for rattling against each other or something else.

 

[Joseph Garcia]

A heat shield rattle won't necessarily rattle all the time. Frequently, it starts to rattle when a vibration somewhere in the truck (like a WOT acceleration) hits a frequency with which the heat shield has a harmonic compatibility, and then starts to rattle.

 

[rockola1971]

First thing I would do is check the transmission line routing. Make sure they were installed in the factory route and mounts. Probably have one not in its mount and rattling against the body or frame. The fluid pressure (Line pressure) in the lines increases as your engine speed increases. Wont necessarily do it all the time and only at a certain pressure causing a certain vibration frequency(harmonic). Unlikely its a solenoid in the transmission that you can hear with doors closed and driving.