What do you have feeding the magni? When I have Modi feeding Magni, I don't hear any noise until the volume is dangerously high, and I'm using Hd 280s that I've found to be fairly sensitive.
The whole reason I bought the M+M stack was because there was that my laptop sound card's headphone out was very annoyingly noisy, and the M+M stack is (to my ears) dead silent within safe volume ranges.
Now if I feed the Magni from the noisy output of my soundcard, the Magni does exactly what it should, and it sends the soundcard noise through to my headphones...
Now, if I turn software volume all the way down, and crank Magni to max, right as the knob reaches maximum volume, there is a noticeable amount of white noise and I can hear a local radio station if I hold my headphone cable just right. I'd be interested in a technical explanation as to how a maxxed out Magni can magically turn into a (poor quality) FM demodulator.
I expect you know this but you should always have the software and OS volume at their highest as this lowers the amp's noise floor.
I'm afraid I don't know what causes the RFI and when I last asked about the noise I'd experienced none else had come across the problem. Out of curiosity what headphones are you using with it and how long is the lead?