@james_n do you know if the SN3 has a signal ground link to chassis ground? The AVR looks like it’s double-insulated…
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I doubt the SN3 has but I suspect there may be another path via the Rega. AV kit can be variable in grounding depending on what’s also connected to the AV receiver - DVD players, cable boxes etc. One way to see if it is a ground loop is to disconnect the Rega and reconnect the AV receiver - still got a hum ? I 'm assuming there is only the Rega TT and AV kit connected to the amp ?
Re-reading the original post, the OP mentions removing other connections and the hum remains. If this is the case it’s worth trying connecting the ground post on the SN3 to mains earth By making up a suitable cable and see if this stops the hum. A few things to try anyway but slightly off putting if you’ve not had problems before with the MF amp. I hope, AV hum issues aside, the SN3 is sounding better than the MF !
James - yes, when the turntable is connected on its own, its fine. No hum. As soon as the AVR makes contact the hum begins.
What phono stage are you using?
Hello,
Same use as you: Denon AVR X4500H on SN3.
I use an Audioquest Red River RCA cable to connect the 2 devices.
Works perfectly
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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?
I am sorry to disappoint you by saying this,but the ground loop Isolator devices not only isolate the hum but a great amount of low frequencies (bass) as well.
Trust me I tried one two years ago & I wouldn’t suggested it as the solution.
Yeah, was kinda hoping that - since most of the low frequencies will be going to the sub for 5.1 - that the sound will not be too affected.
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A ground loop isolator may well fix the hum, but I suspect the root cause is that nothing is linking signal ground to mains ground - the Aria looks to be double insulated too. Naim’s design philosophy ties signal and chassis ground in one place only, traditionally in one of the source components. (In my system, that’s the CD player, and the other Naim source box is set to floating.) @james_n‘s suggestion to make up a lead to connect the earth pin on a 13A plug to the SN3 chassis ground should fix this - BUT you should only do this if you know your way round a 13A plug! If in doubt, don’t…
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Hello, I have the same problem with a NAD T758 and my Supernait2.
I tried many think but I always have the noise in the two speaker.
I have separated both, Now I have two pairs of speakers, one for HiFI and one for home theater.
So, a quick update.
I received the ground loop isolator yesterday and tried hooking it up to both the Denon end and the SN3 end. Sadly the hum persists but no problem - I can return the isolator.
I spoke with a Naim technician this morning and he confirmed it is a ground loop hum and that I should try running a copper cable from the ground socket on the rear of the SN3 to the RCA jack on the rear of the Denon where the SM3 plugs into. Will try giving this a go later.
Hello xfilian, can you give more precision where you have to connect the cable on the rear of the Denon.
Is it on the ground of the RCA plug ? on both plug ? Thank you.
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A shame about the isolator but at least it seems that a ground loop isn’t your problem. I’m not quite clear what adding the additional wire will do. From what you’ve described it’s adding an additional signal ground path that is already there between the two units via the interconnect.
If that doesn’t sort out the hum then try the SN3 ground terminal to mains earth connection. Here is one I made a while back to fix a similar issue between a Sonos connect and my Nait 1.
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James - perfect sir. Wired up the plug as you have above and placed the end on the ground on the SN3. Hum instantly gone. Now screwed in place and enjoying the amp with a quiet background. Thank you and everyone else who contributed.
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Good news - the SN3 will be staying then 
Yep pretty sure she is a keeper 
. Now do I get a new one or beat them down on price on their demo unit?? 
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Thank you james_n, I have to try, it is for the next week-end.
I took the time to do the test, but unfortunately now I know what is a real HUM 
and I hear it when I plug the ground on my SN2 or on the NAD T758 v3.
So, what I hear is not a HUM but it is a sizzle only when I switch on the AV button.
Have you an idea what happen? 
Hi Pierre - apart from the Nad, what else is connected to the Supernait ?
I have been through this and the difference between a “buzz” and a “hum” is either absence of any ground or a too many ground connections (ground loop), but I am darned if I can remember which way round it is. I THINK the buzz is no ground. Years ago I had the same issue with my SN1 and a Yamaha AV amp, the situation was only solved by replacing the Yamaha with a Denon. But given that you already have a Denon, that is clearly not the answer.
Have you tried grounding a spare RCA input on the Denon?
If when switching to AV on the SN3 is enabling an input with no ground, this may provide the required ground connection?