They are not the quietest of engine I expect due to the their racing history and the fact they where designed with performance being the key objective (over 100BHP per 1000cc), I have a 440i for my every day use and that is very smooth and quite but it only achives over 300BHP due to turbo charging.. The reason I had the Vanos seals done was due to rough running at low revs and the failure to tick over.
On the gearbox front I currently have it in with a BMW specialist who has diagnosed detent springs I guess i did not notice the how poorly defined the gate was so, I have decided to have them changed and do the clutch and flywheel as 97k on a 22 year old car is a reasonable mileage for a clutch and it will never be cheaper now I have the box coming out to do the springs.
The joys of motoring,