Supersonic Fuzz Gun oscillation/squelch when gated

[ShameofaNation]

I'm currently trying to fix a Supersonic Fuzz Gun for a friend of mine and it's honestly got me stumped.

The issue is this weird oscillation/squelch noise that happens right after you stop playing when in the gated mode. It doesn't happen when you play softly. It happens across almost all knob settings, nothing seems to be indicative of what's causing it though. I've gone through all the connections and everything is good. All the transistors seem to be working just fine but I tried replacing them with new ones as a last resort, made no difference.

I've only got a handful of repair jobs under my belt and this is the first I can't figure out. Am I missing something obvious? There's a schematic and video below so you can hear what it sounds like.

https://www.youtube.com/watch?v=6J7b5I5lRcA
http://2.bp.blogspot.com/-znDD59ulovI/TxdhUN-MnnI/AAAAAAAAAng/uoII_zb2Tik/s1600/supersonicfuzzgun.png

[anotherjim]

Assuming it was working?
Check off board wiring - nothing broken and control pots work.
With this kind of thing with deliberately reverse transistors Q1 & Q2, check that nobody has looked at it and thought "hey, those transistors are the wrong war around - I'll just fix that" because fixing that will break it 

[ShameofaNation]

All transistors are oriented correctly and the offboard wiring good too.