Andy - A Rega Aria.
I have ordered a ground loop isolator from Amazon. A quick read through reviews shows that a few people claim the isolator may cause a drop off in bass but since most of my low end as far as the AVR is concerned will be going through my sub I am hoping this will not be a problem. Does it matter where the isolator is placed? AVR end or SN3 end?
Aside from this issue, I am enjoying the SN3 greatly. When I first hooked it up it sounded very, very harsh but I have left it running in the background for a few days and that harshness has now gone to be replaced with a beautifully detailed, well rounded, punchy sound. Think my MF may be up for sale if I can resolve the hum issue 
Does anyone think a DIN connection would help matters?