if i drive above 60mph and then take my foot off the gas so it strts decelerating, there is an evident rumble.

i have had all the wheels balanced so its not them.

any ideas?

my car is a 2004 530d auto

 

I can feel the rumble on the transmission tunnel

anyone got any ideas?

 

Slip your transmission into neutral [carefully] to see if the rumble decreases - that would help isolate engine involvement. It could be something simple - but important - like a motor or transmission mount. Sometimes even a physical inspection of the mounts is hard to detect a broken one because the drivetrain weight keeps them in place. You might need some jacks to raise motor / transmission to inspect them.

One other item, though it's rare lately, is a driveshaft gone out of balance.