My P-Bass Deluxe (active) is making a REALLY bizarre noise whenever I have been playing for a few minutes. Here's an mp3 of it: https://www.dropbox.com/s/kvwcq1szmy...ss%20noise.mp3
That file is a recording of the noise, then me unplugging and replugging the bass. You can hear that it takes a second to start backup, but then ramps up to the final high sound.
The noise is controllable with the bass' volume knob. Any notes played during the noise come out distorted and quiet in comparison to the squealing. The squeal goes away with the volume knob all the way down or the battery taken out. As you can hear in the recording, unplugging the jack remedies the problem for a few seconds, and then it comes back with a vengeance.