Like a few others on this forum, I try to give advice when asked. But in 52 out of 57 posts to this forum , the forum member with the problem hasn't even acknowledged my response. I may be old-fashioned but I hope it sure ain't a sign of the times because if its is then we no longer live in a community.
End of rant.

HI!! It has been a while since we crossed posts. I am still fighting the AC rumble on my '99 2.0 auto following compressor, filter/drier, and expansion device replacement. It has been driving me a bit crazy since August--especially since we were so meticulous in our work and used professional tools, digital scales, etc. Since it actually rumbled after the engine was shut down, I believe the problem may be in the expansion device--I have several updates in other posts. The problem is not as pronounced as immediately following the replacements.

I remember you saying in a note that you lived in the tropics--any ideas??

And, by the way, both in advance and for all the other posts you've taken time to do--thanks--you have helped me on many tasks.

The problem seems to be the expansion or TX valve as you indicate. Maybe the evaporator coil inlet (where the valve is located) is touching the bulkhead and amplifying the noise (which is normal as the liquid gas will continue to pass thru the TX valve till pressures are equalised).
I wouldn't worry about this problem as it is pretty normal up here - sometimes the bubbling can be heard for 30 seconds or so after shutdown.
You could try changing the TX or expansion valve as its possible that it is partially blocked (they do wear out).
Good Luck and regards