So something else you could try regarding the cell tower. Install one end of a Z5U cap to each tab on each RCA jack. Twist the free ends together, then run a wire from those ends to the ground tab on the IEC power entry module.
Hey Paul, so... I had more or less given up on getting rid of the last night until one night when I heard it, whilst in bed and with ear plugs in. It must be tinnitus that sounds similar to RFI. I feel like a bit of an idiot but figured I'd come clean in case there are others out there chasing after the last bit of noise.
For what it's worth the diodes and tube shield did have a measurable difference on noise floor/RFI reduction, but the last bit was definitely in my head/ear.
