60 cycle hum

it probably has something to do with the cheap amplifiers you are running it through, i've never heard of a problem such as this.

Cheap aint nutin to do wit notin where hum is concerned. Anyway Yamaha aint cheap, its mid-fi. And I never heard them do that. But 60 cycle is a cooky animus. You could try breaking it all down and re-connecting. I do not know Rega by experience, only reputation, which is relatively very good; does it have a ground wire? Try a cheater plug to break a ground loop (if there is one). First the receiver to the wall, then the table.
I had to get 8 foot grounding rods from Radio Shack to fix mine. And if it does not rain in two months, even that does not work.
Failing that, borrow somebody's receiver. If that works it is probably too expensive to repair your Yamaha. Get a Rotel if you need the tuner, else a Creek, or even an Onkyo.

Aceto has good idea and make sure that cables areb b not too close to each other or power supplies.Think PS Audioo make a device called humbuster but not sure how it would work with yout dry up.
Chazz

High output cartrdiges like the Exact are going to have some "noise" associated with them when you crank the volume on your amp up.

I'm a bit perplexed by the responses from Aceto and Readster. Your analog input is never going to be as quiet as, say, your CD input. It's not a problem though unless it's above the noise floor of your cartridge when playing.