IMO, your suspension will only make noise when the car is moving. The engine and Trans combo does not move enough when placed in gear at a stand still, to compress or expand the suspension.
Since it happens when you put it in gear, and, I assume, when you accelerate/deccelerate as well, I would think it is a bad mount, Lower Engine mount or Trans Mount. Could also be your CV axle. But I would definitely be looking at the things that move, or are made to resist movement, when the Trans is engaged. The lower motor mount is between the engine cradle and the engine.
To check the motor and Trans mounts, have someone in the car with there foot on the brake. Have them shift from drive to reverse as you watch the engine. The Top of the motor should move a little towards the firewall in drive and towards the radiator in reverse. 1 to 2 inches MAX! More than that, you have a bad Dogbone. If it's the lower motor mount. The engine will move but you can see that it's moving at the bottom while the top, the bolts that go thru the dogbones, don't move. If it's the trans mount, I think the drivers side of the motor will move more than the passenger side. But I'm not sure about that one.
At any rate, I think it's one or more of your mounts. The CV axle will only clunk when you engage the trans and ALL THE TIME while you are moving. But I would check them anyway just to rule them out!

 

All mounts have been changed (dogbones, engine, and transmission (actually, I will have to recheck the dogbones as they are 5 years old now and I'm quite heavy footed)). The CV is not bad at all. This is why I think the noise may be synonymous with the service bulletin that suggests the noise is from a bit of slippage at the rear sub-frame mounting hardware. I'll check the torque on those on Monday or Tuesday.

It will be some time but I will post a video of the engine movement while someone shifts from D-N-R-N-D with the foot on the brake. You can tell me if it's too much.

This is one car I am NOT giving up on. I love everything about it except the plastic coolant elbows (new ones on the way).

 

I know how you feel. In the refurbishment of my 02 I have spent way more than the car is worth, in repairs and I am still working on it. It will be don't this spring, mechanically at least. But I Love my Monte. Only thing I would change is from the 3800 Series II to the V8.
If all your mounts are good then the cradle/frame bolts make sense. As I said, it has to he something that moves, or resist movement, when you engage the trans.

 

Ah but to climb under the subframe when the engine is running and have someone (someone I REALLY trust) to do the N-D-N-R thing...... *shudder*

Jackstands, ramps, blocks, more blocks, and last and least (at least in stopping power), the e-brake. Ooo.. Maybe I'll strap it down dyno-style, too.