I have that issue...I only get hum when the dimmer lights in my kitchen are on. I tried lots of things to eliminate the problem and in the end I just leave those lights off
Regarding clamps, the reason the VPI clamps work so well is that they are an integral part of the design. In conjunction with the platter design they create a very slight vacuum that holds the record down to the platter in addition to clamping it. Very effective.