Clipping is a special case where the final p-p amplitude exceeds the supply capability. More commonly, low frequency audio requirements overload the supply filtering below the differential needed for regulation. Then, you're effectively modulating your power supply. No well designed amplifier will go out of regulation at 114 VAC.
My stand-in Dad complained about noise he was getting on his Wave Radio, located in the kitchen. I told him that we could find out if it was line sourced or radiated. I built him a filter using a 4" box, single duplex, 3 or 4' 12/3 plug and cord, and a Corcom line filter. It solved his problem so we lucked out and explored no further.
Some power supply designs lack sufficient high frequency bypassing. Huge filter caps prevent clipping but have high equiv. series inductance that lets hi-f noise right on by. If additional line filtering reduces the noise you're hearing, then the supply would be suspect. If not, then it's time to try isolating the inputs, re-orienting the amplifier, checking the headphone output, Et,c.
Joe
