I presently drive an '02 M3 Convertible and love the way it
drives and looks, but with the top up it sounds like a
stagecoach from the old west. Thinking about buying an S4
Cab - any problems with top noise to report?

 

not here. i have the 05. haven't driven in rain yet. hope it doesnt leak.

 

I've an 05 as well, and the only problem with it is that I can't really hear the engine (I like the sound). I believe the 04 has the same roof, so you should be good to go.

Really, I've not noticed anything 'unfortunate' about it, it has no noticeable shaking, the car is a lot quiter than my non-convertible 01 Camaro, as near as I can tell it's about what you'd expect from a regular tin-roof, except you have the option of folding it away. Well worth the extra dinarii.

NTM