There are a lot of postings on the topic of RFI at various audio websites. I'd like to include my version in case somebody else gets driven nuts (like me) trying to find just where the problem is in their system. I transfer vinyl and tape to CD. I'd like to remaster or master for real bands but everything in due time.
I went to a few audiophile websites and picked up the buzz about this moving-coil cartridge for a turntable tone arm made by a Japanese company called Dynavector (the 10X4 mark 2 $350.00) The reviews said that this cartridge rivaled those costing $1000.00s in performance. I got it and installed it.
About a week after doing this, I started to pick up a 66 Khz AM radio band faintly coming out of my speakers. I was recording this station with the audio from the vinyl. At first, I thought that I needed to buy expensive double shielded cable for my system. I took apart my whole system starting from the PC audio card and started reconnecting cable, preamp, more cable, turntable and finally snapping on the cartridge. The cartridge was the problem. I had also a moving-magnet cartridge for my 78 rpm records from Grado but it didn't produce the problem. It was specifically the "moving-coil" cartridge. I surfed the net and found an article that said that moving-coil cartridges,even the ones that cost $10,000.00, are sensitive to RFI.
I consulted with Dynavector tech support, with Audience tech support (makers of the best audio capacitors on the market - Auricaps) and with an electronics engineer who specializes in audio electronics, who wrote a few articles on RFI in circuitcellar magazine. Each one had his own spin on what the solution should be. I went with the advice from Audience which was to go to Radioshack and get two minidisk ceramic capacitors within a 40pF - 200pF rating range. I chose 220pF. Then solder each one to the left and right stereo leads on my tonearm headshell.
It worked like a charm. Now I have - 69db background noise on my software peak meters. I turn up my speaker volume to max and don't hear a thing, not even hiss. The records play back great. Total cost for this repair $2.00.