why is my crate FX 120 watt guitar amp buzzing?

when i turn on my amp it just buzzes. ive tried different chords, direct plug in, took out the pedals, checked the wiring, plugged into a new outlet. its just buzzing. its a combo amp so there are no tubes. no cracks, no rips in the speakers, no loose bolts or nuts, the buzzing is on clean and distortion and you can hear it very well. the weird thing is that when i palm mute the e string and then tough the end of the chord that is going into my guitar , the buzzing stops but as soon as i take my hand off the buzzing is super loud.