Speakers cut out when braking

I'm driving a 2002 325ci with the HK sound system. As far as I know, everything is stock except for the head unit, which I believe was swapped for a 2004 model. Since we bought the car a couple years ago, there has been this weird issue where all the sound will cut out when you press the brakes. It used to only happen occasionally, like once or twice on a drive, but lately it happens every single time I push the brakes and it's driving me crazy. It generally cuts out for 1-3 seconds, it cuts sound off from all speakers, but does not cut power to the head unit. The music continues when the sound is gone, so portions of music is missed.

I'm guessing that it is probably a wiring issue, but before I start tearing my car apart searching for a bad connection/bad wire/etc, I'm interested in hearing people's opinions on this problem. Has anyone else experienced this problem? If so how was it fixed? Anything else that could be causing this problem (bad amp?)?

Let me know if you need any additional information regarding the issue to make suggestions.
Thanks!

These cars of ours are electronic nightmares. Try disconnecting both leads of your battery and shorting them together for 10 minutes. It's quick, it's easy and it's free. I had a similar problem - sound from the rear tweets only UNLESS I was making a right run. Pulled the amp and checked everything - NADA wrong. Someone suggested shorting the battery leads together for 10 minutes. WORKED!!!!!

I'm in awe. At first I thought the battery trick you mentioned was crazy and would never work, but I did it this afternoon and haven't had sound cuts out since. I also replaced a speaker at the same time though, so it's possible that was the real fix, but either way I am now very happy with my stereo. Thanks!