I went through the buzzing toroid issue a while ago, that's why the amps were in the furnace room and not the listening room. I tried everything to get them to stop. The common thinking on line is you have a DC component on the line. I didn't. In the end I took the Dave Berning approach and am using switching supplies. They grunt a little when charging up the rail caps I left in the amps but are silent after that. I just finished a pair of mono blocks yesterday, one stereo left to convert. Here's the SMPS I'm using, set for 120 VAC not 230:
https://hifimediy.com/power-supplies/diy-power-supplies/SMPS800RE-72V-230VThey have larger and smaller models. For the stereo amps I'm replacing 1600 VA transformers with dual secondaries. I use two of these in those amps. The mono blocks have a 1600 VA toriod for one one channel. I don't expect to be driving any one Ohm loads so I didn't see the need for the 2000 Watt SMPS in the monos.