Hi!
I’ve found that lots of people are struggling through the noise issues with different Naim amplifiers. Last week I acquired the brand new 5si and faced the very same thing. I should say it is a totally exhausting experience. However, I managed to find quite a working but an exotic solution.
At the moment I’m using the well-known WXAD-10 as the main source. When I turned on 5si for the very first time I heard some unpleasant noise when the volume was at 11-12 o’clock. Needless to say, I was immediately hit by the blast of fear, emptiness, and despair. When I added a sub to the system, things became even worse - an unpleasant noise at 9 o’clock. Luckily, there were no one nail in the wall and no rope that able to hold the weight of an adult pig 
When some thinking returned to my brain, I remembered that I have a small bucket full of smartphone chargers. I started trying them all and found that the one, from Yamaha, was the worst. Some were quite good, Sony, Xiaomi. And one, from Samsung, was just excellent - the noise significantly reduced(sic!) when I connected the streamer using this adapter.
I have no idea how come that happened, but the fact is that the noise becomes audible about at 3 o’clock which is good!
To check things twice, I dismantled the system, started from the amplifier without any input connected. The audible noise at 11-12 o’clock. Adding WXAD-10 with the Samsung adapter decreases the noise as if it produces the noise of the opposite phase. However, adding sub makes things worse.
I once tried to replace the WXAD streamer with Node 2i and had another blast of fear, emptiness, and despair. So, no more experiments with Node 2i I’m staying with WXAD until I find something significantly better.
A couple of things I added later:
- Plus power filter and that reduces the noise a bit
- Minus sub. Need some time to think if I really need this guy for my Spendor 3/5.