Need help with Hum from a Big Muff

[Angle Loss]

Hey guys,
I need your help with one of my projects.  I've built a Big Muff Pi clone off of a General guitar gadgets board.  I've been tweaking the circuit for the right tonal response.  The problem is that there is an ever present hum--a lower frequency hum that does not go away.  To be clear, this is not noise from the fuzz.  I've had a handful of green, lambs head, nyc, and little big muffs in the past to compare.  If anyone might have suggestions where to start to fix this.  This hum is present whether powered by adaptor or battery. 
Thank you,
Chris

also, if anyone has a schematic for a blue/silver russian or early green (tall skinny letters+bad paint) sovtek muffs I'd appreciate it.  I've seen the tonepad schem, but I believe that is for the later bubbly letter green one.  Thanks!

[RDV]

I eliminated all the ground loops in mine using shoulder washers to isolate parts I didn't want touching the box. It helped, but still makes some noise. It's a high-gain circuit. If I don't turn the gain all the way up it helps a bit.

RDV