2007 Lacrosse CX 3.8 Series 3 w / 95k.

I bought the car a little over 2 years ago with 34k on it. I had it about a year when I started having a trans issue. From a dead stop in forward or reverse, I get a single, loud clunk. It is extremely random. I can go two weeks without it happening, or it can happen several times a day. I changed the motor mounts, nothing. I took it to a trans shop to talk to them and have the fluid changed. They said that unless they could get it do do it, they would have no way of diagnosing it. There was no sigh of any metal, fluid looked good. It sounds like it is coming from behind me, but there is nothing back there. Other than that, the trans is great, no other issues. My main concern now is; I have a little less than one year left on the warranty. I would like to get this fixed before the warranty runs out. Does anyone have any ideas? Thans for your time.

Do you feel anything associated with the clunk?

Not a thing. Other than that, the trans is perfect.

What do the engine RPMs do during this event?

Nothing, it happens in less than a second.

What speed is the clunk? From zero to 5 or higher?

It only happens from a dead stop. As soon as you touch the gas, BANG. Forward or reverse. One thing I haven't checked are the dogbone torque mounts. I don't think that'* it because it sounds like it is coming behind me.

Check for a bowling ball in the trunk.

If none are found, check the rear suspension for forward/backward play. Might also want to check to see if a brake caliper is hanging up or something like that.