I looked at the manual of this naim amp:
"3.4 Radio Interference
In some circumstances, depending on where you live
and the earthing arrangements in your home, you may
experience radio frequency interference. Controls on
broadcasting in some territories allow very high levels of
radio frequency radiation and both the choice and exact
siting of equipment may be critical. Susceptibility to radio
frequency interference is related to the wide internal
bandwidth necessary for high sound quality. A radio
frequency filter kit is available for some Naim equipment but
sound quality will be progressively compromised as more
elements of the kit are fitted."
Maybe this can also help?