Why does the break warning light and a chime go off every 15-30 seconds while driving?

This does not happen when you are actually pushing on the break pedal, the problem seems to be completely independent of physically engaging the breaks. The master cylinder is completely topped up. The breaks respond and act fine and there does not appear to be any drag. It is not a consistent problem, sometimes it will go as long as 3-5 minutes without the lights flashing and the chime sounding, other times it is every couple of seconds. This does not seem to correspond to any particular driving act. Additionally though possibly unrelated, the same day this started the engine started throwing the code for low voltage to the throttle position sensor. Any suggestions?