Counterpoint SA-5000 - phono stage question

I've had the Counterpoint SA-5000 for many years. Just recently got back into vinyl and while the overall sound is fantastic, there is a hiss that begins just past 12 O'Clock on the volume dial. It's not audible at my normal listening levels, but I want to get to the bottom of it.

Seems to me that it is coming from the MC side of the phono stage (my turntable has an MM cartridge). It's not from the turntable itself, because I unplugged the RCAs as well as the ground and its still there when I select MM (and of course on MC). Worse, with MM selected I played around with the MC load dial and I could hear the click loudly through the speakers. In fact, which MM selected, I get the least noise when I select the least load (100) and the hiss gets progressively louder as I increase the MC load. All this while MM is selected, so the MC side of things is obviously the culprit here.

Would be grateful if anyone could shed some light on this and possible solutions. The one solution that has been suggested to me is to short circuit the MC by using shorting RCAs - is this safe?

Thanks