"Some" is probably an understatement. I'd wager most of those who use their N900 for FM radio, web radio, or local music playback have encountered this on multiple occasions.

It happens very frequently for me. I guess renicing apps might help but i haven't tried that. Basically, whenever i am using N900 while music is playing, i expect to have a few blips or stutters. It doesn't usually happen if it's just in my pocket.