Supersonic fuzz gun clone volume problems

[944cabby]

I've just built a poodlepedalparts clone of the supersonic fuzz gun, and while all of the knobs etc work ok, whenever i play a note the volume seems to increase and decrease intermittantly - so if i strike a note it will suddenly go very loud and then low and sometimes the fuzz signal will be lost.
Anyone got any thoughts as to what may be the issue?

[944cabby]

Forgot to say, the led works fine and theres sound in bypass mode , although when you switch to oscillation mode it just sounds like a tractor.

[LucifersTrip]