As @jea48 mentioned, the RFI could be coming from somewhere else in the house. What is upstairs, directly above the MFR-260? And by any chance are you using a cellular 5G internet access point in the house?
Just a thought...
Improve RFI
I have terrible RFI in my basement system. The RFI indicator on the Universal Remote is always on, regardless of where I locate the sensor, and I have to revert back to using the individual remotes for AVR, Blu Ray, etc. I also have a surround sound system on the main floor; same AVR, same universal remote, and no RFI.
The kitchen is on the main floor and all appliances which are usually identified with RFI are in the kitchen. The lighting is different in the basement and the washer-dryer and firebox are in the basement.
Everything I can pull up on RFI seems to be from the ham radio world. They constantly point to the firebox but there doesn’t seem to be any consensus on how to deal with it.
Any help would be appreciated