03 GMC Z71 SLT metal sound in rear

[smokeymacs]

My 03 has almost 300,000 miles and does not make the noise constantly. It only does it when the AT is in drive, it's sorta a rattling sound like rocks in a Pot-metal bowl or something. I can be cruising down the raod and put it in neutral and rev the motor, no noise. I put it back in drive and it seems to come and go every few minutes. Any help before I start swapping out parts? Thanks in advance.

 

[Z15]

The first thing that comes to be is the flywheel or flex plate. It might be cracked. We had a truck at work once that had similar noise and thats what they found was the problem.

Of course just is just a wild a$$ guess

 

[smokeymacs]

Yeah I'm starting to think it's not all the way in rear, maybe sounds to be midway through the truck. At first I was thinking cat broken up, but it does'nt do it in park revving the motor, thanks