well i cant comment on the sound either, mine does something a little bit similar, when i back up sometimes i will hear a faint grinding or groaning sound and sometimes my traction control will kick in for no apparent reason, and like you said it goes away and never comes back again...I cant explain it.
Maintenance-wise the 3.8 is a darn good engine, and the only major flaw it has is the upper intake manifold, which is prone to failure, and most mechanics will diagnose it as a failed head gasket and replace that instead, costing you a lot of money for something that you dont need.
If you enjoy reading, there is more information than you could ever want at this link:
http://www.bonnevilleclub.com/forum/...e=article&k=38
I know your Intrigue isnt a Bonneville, but its exactly the same engine, so all the info mentioned there applies to you just the same, even if you dont work on your own car it helps to be educated, so when your driving along and your car all of a sudden overheats and then wont start because its hydrolocked...youll know to immediately drain the oil and find someone to fix your upper intake, as well as the lower gaskets
instead of paying out the butt to fix a head gasket, and still having a 3500lb paperweight.