Double Flush thumping - need help

[rockprocess]

I just completed a double flush build and everything is working fine, except for a loud low end thumping that matches the pulse.  Any idea what this is and how I can eliminate it?  It's not a ticking per se, but rather a low end thumping.

[midwayfair]

Is everything else working as normal?

and

How loud is it, and does it change with the depth?

and

Are you using single coils or humbuckers?

[rockprocess]

Yes, everything else works as normal.  It does get louder as you turn the depth up.  Overall its a very loud thumping, you can't use the pedal until I get this fixed.

[rockprocess]

Ok, got it sorted out.  Basically my led for the optocoupler was for whatever reason way to bright.  I added a trim pot instead of the minimal resistance value in series with the depth pot and dialed the Led more dim.  This brought the thumping way down into the acceptable range.  I guess that's the risk you take when you make your own optocoupler!