No, it's not the heat shields. Those have been off for a long time. And it doesn't seem to be any of the accessories - PS pump, alternator, compressor. etc. I get a funny rattling that is slowly getting worse that is coming from the engine compartment, but it seems to be coming from the engine or maybe the transmission. It's hard to locate the sound. Although it does sort of sound like a heat shield rattling, it's not that. The way I could also describe the sound is that it sounds like a bad timing chain on a car with a timing chain. But a little more intermittent.

The latest thing I've noticed is that it seems to only happen when the transmission (auto) is engaged, and not when it's in neutral.

I know that the motor mounts need replacing, and that the engine shakes more than it should.

Anybody have any ideas what it could be? Is there a serious engine problem that sounds like what I'm describing? Or something with the tranny? Thanks for your thoughts, this is sort of stumping me.