I agree with the RFI diagnosis. I had a similar problem in a previous (high RFI) location and the problem had to do with direct sight lines coming through the windows. Things you can try (those blockers did nothing for me): 1.try rotating the pre-tuner 90 degrees
2.hold up a piece of steel (baking sheet?) between the pre/tuner and the windows and see if that affects the RFI
3.if it turns out that #2 does affect the RFI beneficially, but steel between the source of the problem and the pre/tuner is not an option, you might consider relocating the components to a completely different location - I had to literally have my system one floor down (which was under street level) with only the speakers above - to really eliminate the RFI
Good luck! It's a tough problem!
2.hold up a piece of steel (baking sheet?) between the pre/tuner and the windows and see if that affects the RFI
3.if it turns out that #2 does affect the RFI beneficially, but steel between the source of the problem and the pre/tuner is not an option, you might consider relocating the components to a completely different location - I had to literally have my system one floor down (which was under street level) with only the speakers above - to really eliminate the RFI
Good luck! It's a tough problem!