When my 1999 E46 328i auto just sits at idle speed in neutral, I can feel a very slight wobble- not enough to wobble the doors if open, but I am aware of it. Any higher revs than idle and the engine immediately engine smooths out.
It has done 53k and I only use OPTIMAX in it- this is a super unleaded petrol here in the UK!
I don't think it is a problem at all, but it is just something that I have noticed.... is it normal? Does anyone else notice this?