1998 Cavalier 2200 Automatic

36,000 original kms...

The car runs fantastic....but when I have the engine idling in park...and only park....I feel/hear this wierd grinding grumbling sound through the firewall/brake pedal. No smells or loud sounds accompany it...just sort of a grumbling vibration...

The second I put it in any other gear...it goes away...the car runs quiet and smooth.

Any idea what this is. It is the 3 speed auto tranny