My Cary PH 302 phono amp MM hum?

I have a PH302 and use the MM input with an external SUT. It has always been very quiet and hum free.

Maybe the transformer input of the MC input is providing a break in the ground loop - I'd still be suspecting a ground loop of some sort. Since I star earthed all my electronics off the same wall socket, I've had zero problems in this regard.

There is a ground lift switch on the rear of the PH302. You could try this, but it made no difference in my setup.

Is the hum in both channels or just one?
If only one, perhaps there is a 'dry' solder joint in the MM input. I've experienced this issue before with another preamp - resoldering a joint on a relay fixed the issue. If the hum is in both channels, this is probably less likely (ie there would have to be 2 faulty joints, you'd have to be unlucky).

Thanks for your reply. Sorry for my ignorance but what is an "external SUT"? Also not quite clear on a "star earth". I do notice a little more noise coming from the right speaker. And it seems less loud when I don't have the TT ground wire connected. I played with the fixed and floating ground and also found it made no difference. Thanks for the suggestions on the on the MM solder joints. I will check those.

A SUT is a Step Up Transformer, typically used for low output MC cartridges.