I've run into this problem on various pieces of equipment and many times the solution is to clean the pots. You won't do any harm cleaning the pots. If you're bass has active electronics, have you replaced the battery? This could cause the problem, too. If you don't remember the last time you replaced the battery, then just go ahead and replace it. Oh...one more thing...make sure you clean the pots on your bass, too.
Even people that aren't into music notice when the bass player stops playing.