Any suggestions for this? i had a ts808 board from general guitar gadgets and built it pretty much according to the schem, but i added the 'fat bass' mod from amz; they already had the holes in board so i figured, why not. whenever i activate the switch (bypassing the cap to ground in the clipping loop) i get this crazy helicopter sound when i'm not playing. if i'm playing, you can't hear it. stop playing and it's like the opening scene in 'apocolypse now'
It used to be called "motorboating". Your circuit is oscillating at a very low frequency. This is usually a problem with power supply decoupling.
However, you might want to read "Debugging Thread: What to do when it doesn't work".