60 cycle hum

I'm running a Rega P5 with outboard PSU into a Yamaha receiver with an internal phono stage. I hear no extraneous noise with the needle off the record 'til the volume control hits 12:00 - it then increases as the volume increases.

Playing records, the Exact cartridge has such a high output that I routinely listen between 9:00 and 10:00 and get plenty of volume...

Is the hum a problem or am I looking for an excuse to buy an add on phono stage?

BTW I seem to recall the same "problem" with an old HK receiver and a Denon TT with a Grado cart........but I thought it was Grado hum and when I swapped the cartridge for an Ortofon it was still there, but only at very high, not listening, volumes.

any comments would be appreciated.
Are you using a VPI Power Line Conditioner to fine tune your speed? The old PLC would cause hum if placed too close to circuitry. Moving it away a few feet would solve this.
the cartridge is picking up noise from the motor in the turntable probably. grado doesn't sheild cartridge says turntable should be, don,t know about your exact cartridge.
The Exact is shielded but will still pick up stray noise from transformers, etc.

Where do you have the PSU located?
PSU is located about a foot to the right of the TT. I've tried reversing its plug polarity and plugging it directly into the wall instead of the monster HTS 2000.
Sorry for the delay, been away for a few days.

If it's below the noise floor of the turntable and only audible when the volume pot is pushed past 12:00 - honestly, I wouldn't worry about it. I can't say 100% without hearing it in person - but it sounds like normal noise levels for your setup.

The number of coil windings in those high output cartridges are going to pick up some stray noise. Every Goldring (6mv) or Rega (7mv) cartridge I've ever run has had it.

You can drive yourself nuts tinkering with all the nuances of analog - your best bet is to just sit back and enjoy it as long as nothing is glaringly wrong.