I'm also running Nod32 and have no stuttering music. If you also had it in other games it might be a driver issue (?)
It might be an issue with Creative's vista drivers, I don't know. In any case they've been updated recently and the issue is still there, so I doubt it's a driver issue on my end. I've seen people fixing the issue by installing a third-party directshow filter, but I'm reluctant to go that route. Interestingly, I've also noticed that the volume settings in my AC3 filter directly influences the volume for the in-game music.
Anyway, I've finally made it to the Broken Steel part with my new character today. When I bought it I didn't feel like playing it with my old character and started from scratch instead.
Unfortunately, I think I'm going to hit the level cap way before I'm finished with all of the DLC packs. I'm level 21 now and aside from Broken Steel, I've still got the Pitt and Point Lookout to go. And Mothership Zeta, obviously, but from what I've seen it looks like a combat-focused corridor crawl, which is kinda disappointing. I'll probably end up buying it anyway, but it's likely the last thing I play of this game unless they decide to churn out some new packs.
Oh, and those new overlords... Christ. Those guys are tough. I got a nasty surprise when I met one while attempting to rescue the Big Town folks and mistook it for a regular super mutant. I think this is the first time since I first saw a deathclaw that I've been terrified of an enemy in this game.