I have a 2007 c6 with t56 and z51 package, when accelerating from a stop by the time the clutch barely engages the front left suspension will let out a single 'crack' noise and a felt soft 'thunk' in the drivers footwell. This occurs every time once the front of the car lifts up maybe 1/2 - 1 inch when accelerating from a stop.

It doesnt seem to affect steering input at all although I can feel it through the wheel lightly. Doesnt occur when turning while not moving unless I go almost to lock.

• Replaced end-links and sway bar bushings, I didnt see any marks on the lower control arms although the non adjustable end links seem...really close. Sway bar is in properly.
• Every other suspension part has 2 years/40k miles on them but they are mostly extremely hard driving backroad miles with sticky tires.
• Mounts are the polyurethane hinson ones replaced 30k miles ago with an engine rebuild. Doesnt feel like drivetrain lash at all though.
• Greased the spring adjuster seats. Prior to doing this it had very recently started making a damaged ball joint metal on metal sound when turning, was just the spring and it went away.
• Checked that all wheelwell suspension bolts torqued to spec. Motor mounts and cradle bolt torque not checked, visually cradle doesnt have gaps between bolt heads although I dont know if that is useful.

This doesnt audibly occur when going on and off gas as long as I am carrying enough forward motion to keep suspension under enough of the same directional load.

Its not from the rear end.

Any ideas/suggested troubleshooting steps?

 

Check the rear sway-bar mounts. They've been known to back-out.

 

They were removed and the bushings lubricated when I replaced all the end-links last week.
I just went for a drive with the climate control and radio turned off. Turns out I CAN hear this noise most times I go from not on throttle to throttle, its not something I feel at that point though due to suspension roughness masking it.

So it is happening with the clutch engaged. Unfortunately I know what the torque tube noise sounds like and its not that either.
The rear end doesn't make the noise. I've had bad chatter back there and the axle nut clunk but that stopped after diff fluid change and new nuts.


It almost sounds like its near the inner side of the front left wheel well near either the top shock mount or the inner side of one of the control arms, or possibly the front sway bar itself hitting something and I'm just not seeing the marking?
If the left motor mount came a little loose is it possible for there is be a crack/dull clunk noise but no noticeable drivetrain lash? Engine slightly lifting against that mount slightly or something and I've just become used to it?
I have the DRM shocks with poly strut mount bushings and they were properly squished to the size of the metal top plate when installed. The top side bushings are still that size but the underside one almost looks completely uncompressed when its in the air.

 

Do you have a remote clutch bleeder that might be swinging around and hitting something?

 

I don't

The speed which it happens is literally 1-2mph; almost immediately as the clutch touches the flywheel before the car really moves forward much. Its during the point where the torque from clutch engagement starts to load the rear and very slightly lift the front while still releasing the clutch all the way.

The noise is like a single dull metallic crack or pop noise like something is releasing quickly from a 'stuck' position, or changing position from a resting position to whack into something.

 

Following. I recently started hearing a similar noise on mine. So far I've checked sway bar mounts/links in the rear and found nothing loose.

 

One time in my 2000, it was rusted splines on the half shafts...