Since this amp employs an EI core power transformer, DC on the line really won't affect it. But if the cores are not secured properly, it can vibrate.
The four screws on the power transformer at each corner might simply be loose. Its worth it to see if tightening them makes the transformer quieter. This probably can be done fairly easily. Of course the amp should be unplugged from the wall, and to best do this the bottom cover removed. If any of this sounds at all tricky, take it to a qualified technician.
The four screws on the power transformer at each corner might simply be loose. Its worth it to see if tightening them makes the transformer quieter. This probably can be done fairly easily. Of course the amp should be unplugged from the wall, and to best do this the bottom cover removed. If any of this sounds at all tricky, take it to a qualified technician.