Ruby Amp - strange distortion

[Ben79]

Just finished building a Ruby amp with a switchable Bazz Fuss in front of it on turret board.  It's built into a 1950s portable radio using the original control panel as a chassis and the original 5" speaker.

It has an odd issue.

The amp can sound fine but presents an unpleasant 'dead battery' kind of noisy/crackly distortion with the gain pot anything above minimum and the volume at anything LESS than ~90%.  Apart from that it's behaving normally.

I've built a couple of Rubies before and never encountered this problem.  

I'll post voltages tomorrow if I get a chance but just wanted to throw this out there in case someone can think of a prime suspect.

[Quackzed]

is it a farty kind of distortion? might be this...
http://www.diystompboxes.com/smfforum/index.php?topic=80505.0

[Ben79]

I don't think so.  i can't open the video but from the sounds of it, that was a voltage problem.  Mine is running off an adapter.  It's odd that the noise happens when the volume is turned down.

[antonis]

Weird case..

It seems to me like a "reversed" input offset voltage problem...