Clanging Metal Sound in Drivetrain?

[JimmyTwoToes]

The vehicle in question is a 2008 Tahoe 2-wheel drive and an automatic transmission.

The noise itself sounds like a rotational metal on metal sound. Clanging with intensity mirroring accelerating.

It takes no effort at all to reproduce; put the car into drive and step on the gas. The truck will happily move forward, making that drivetrain sound in both drive and reverse. Even putting in drive and mashing the brake so the wheels don't move.

Here's the thing..

1) If you're in park and step on the gas, there's no sound.
2) If you're in neutral and step on the gas, there's no sound.
3) If you let off the gas and coast, the sound goes away immediately. Step on the gas again, and it comes right back.
4) There doesn't seem to be the sound at highway speeds (but maybe I just can't hear it).
5) The vehicle performs normally with no codes.

It seems to be completely in synch with the gears. It does this equally whether cold and warmed up.

I looked under the truck and don't see anything obvious interfering with the driveshaft.

Any idea what this could be? Started out of the blue yesterday.

 

[swathdiver]

Put a wrench on your torque converter bolts.

 

[HiHoeSilver]

And take a peek in the inspection holes.

 

[JimmyTwoToes]

Thanks. So please help me understand the physics here. What is exactly rubbing against what? Can this be driven until I get this done? (Can't do it myself). Is something just loose and is it dangerous or damaging to drive it or just an annoying nuisance? My commute puts me on the interstate to and from. Thanks again.

 

[swathdiver]

The torque converter bolts up to your flex plate/flywheel. I think there are three bolts and if one gets loose they make a heck of a racket like banging a night stick inside an aluminum garbage can.

You should tighten them right away as if a bolt or two backs out and falls away, the others are likely to shear off. That said I and others have driven home gingerly until we could put a wrench on them. That is of course if that's your problem! Can't really diagnose that over the internet.

Drive it up on some ramps and crawl under and have a look around. I don't know what size wrench, I think 14mm or 15mm but someone here will know for sure.

 

[iamdub]

^^^What they said. The sound can happen with the driveline being in gear (under load) and not when it's out of gear (no load). Cracked flexplate can have similar symptoms. I'd say it's unlikely in this case, but it could also be busted U-joint, although this usually presents symptoms you'd hear and feel long before getting to the clanging stage.

 

[Scottydoggs]

drive shaft u joints are easy enough to check, get under it and grab the shaft at the ends twist it back and fourth, the middle X part should move with the rest, if it clicks and you feel or see it move the joints bad. hand holding the yolk, hand on the shaft, twist opposite directions back and fourth.

bad u joints usually have a damn good vibration when your in the gas. either side can fail, but ive replaced more axle side joints.

 

[JimmyTwoToes]

"banging a night stick inside an aluminum garbage can."

Thanks, everyone. The thing is, it's not that terribly loud. If the radio is on or the fan on high, you can't hear it over that. I generally have to open the window and stick my head halfway out to hear it. It sounds like something metallic is hanging over the driveshaft, but I checked for that. Does that change anyone's opinion? Thanks again for all your feedback.

Also, I feel nothing. The vehicle is driving perfectly with zero vibration or slipping.

 

[iamdub]

Have you checked the flywheel and converter bolts or anything underneath it? Maybe someone is pulling a prank and wrapped zip-ties around your driveshaft.