I'm going crazy with this issue, after recapping the radio works perfect, clear and powerfull sound. Tape source has an horrible screeching sound, I was reviewing mech earth, caps solders, tape/ radio and Rec/Pb switchs, all seems to be ok, desoldering head's ribbon the issue continue. Recording from radio the sound it's ok. It's like the mic introduce a parasite signal. The screeching is very high, at 0 volume level you can hear it, and at 2 level is almost unbelievable. It must be an common issue, I have another donnor unit with the same problem. Any Ideas?