[PaulR]

To go back to the start, I found that my pantry transmitter was becoming more and more unusable due to RF rubbish from SMPSs. Putting a class x capacitor inside a 13A plug and trying it in different sockets helped immensely and has made it possible to use it again. It didn't help for LW, though.

A bluetooth receiver would use the full potential frequency response of the amplifier so would sound a lot better than using a pantry transmitter, and be an interesting modification, but it might be worth trying to see whether a capacitor in a plug helps with the interference problem with other sets. Just be careful of the small charge held in cap if you unplug it!