rockerverb 100 hum

[dcw1385]

I recently purchased a used rockerverb 100. I took it to a tech to have it checked out. He said everything was ok but he said wired a ground to the chassis and that I could have been shocked. I'm not sure if I didn't noticed it before or if the volume was low when I originally tested it out, but now there's a significant hum(really loud) whenever the gain is past 12 o'clock. I've tried several different variables, guitars, cabinets, cables etc. and nothing reduces the hum. I'm suspecting it has something to do with the ground he added but just to make sure, does any one else's rockerverb 100 hum significantly more when the gain is past 12 o'clock? Just looking for some input before I head to another tech.

[hairmph]

Could be a ground loop. I would have a different tech check out the amp, if you haven't already.

I bought my RV50 used and it is the best amp I've ever owned!