blackout digitech metal pedal farting! Help!

[Rich#6]

I have a guitar with a blackout(18v) and running it through my digitech metal pedal it farts, as if the signal is failing underneath the distortion. almost a double sound. It does this a little on my model 6 with the midboost if I let a chord hang on both my pedals( I also have a uber line 6). the blackout guitar only does this with the one pedal. No other guitars have problem on the digitech. It just started this too.
Help!

[Grandturk]

Could the output from the pickups be clipping the pedal? That means the input is too hot. See if adjusting the level on the pedal down helps... see if rolling the volume down on the guitar has any effect.