super duper 2 in 1 transistor fail

[r0ckinrandall]

Friends,

   I am working on a super duper 2 in 1 circuit and I am experiencing a soft, whirring, white noise behind the correct audio of the pedal. The effect, gains, pots.. etc.. are all working, but there is an additional noise present. First, I changed the caps, but there was no change. Then the fun part...

I changed the bs170 transistors.. and the problem seemed corrected... until I heard a soft pop about 1 minute in and the issue returned.

I can't get to my meter until tomorrow.. any thoughts or guesses now? What could cause the transistors to fail? Everything else seems ok.

THANK YOU ALL.