Paul Cochrane timmy crackle

[dan9]

Hello all, having just started building my own pedals (A massive thank you to all the contributors to this site). I've been having some problems with the Timmy clone I built. its build using the first veroboard design on this site using components from one of the kits from bitsbox.

The problem is when i turn the gain down and strum hard I get a crackle/breakup, it seems to be in the high frequency range as if i cut the highs and max out the bass it goes away. with the gain past 12 o'clock you cant really hear it for obvious reason.

I've checked and double checked everything is wired correctly and all the solder joints are good and I cant figure out whats causing it, any pointers would be greatly appreciated.