Ok!

Today I noticed for the first time, a loud rattling type noise with the car in neutral.

I turned down the radio and could hear it clearly, once i turned off the A/C the noise went away, turned it back on, the noise re-appears.

However, once i engaged the clutch to move off, the noise went away.

What could this be or related to?

 

if there was just noise with the a/c on/off then I'd say it was the magnetic clutch on your a/c compressor. Since it goes away when you press the clutch in not too sure. Is there no noise at all when driving normal, or slow?

 

I had the same exact issue! The dealership attempted to fix it twice. The 1st time, they replaced all my tranny bearings. When that didn't work, they replaced my clutch/fw/pressure plate. That got rid of the issue for a while but I think it's back again.