Oh dear, does the 320 sei petrol auto have similar issues? 2001 plate

Mate picked one up last thursday. It was fine on the test drive but never went above 40. On the way back we stopped and he said it kind of grumbled a bit and the revs dropped down.
So from what mark says the rev drop is normal, grumbling is not.

He said he has not noticed it since, but not used the car much either.