Trying to identify noisy component

[hypnodrone]

I have a tone bender variant (Burns / Baldwin Buzzaround) that emits a quite loud background noise. Does anyone recognize the sound in the video clip. The effect in itself sounds wonderful and everything works, but the crackling noise is very audible when not playing.
The clip is just the populated board with jacks and a battery. No swithing or led involved, to eliminate wiring faults (test wiring has been verified). Cable is not connected to input (makes no difference in noise). Could it be a fried transistor or diode?
I have killed parts before, but I have never had this noise.