I've had this machine for 30 years. Used to do 4 track live recordings of a band I played with feeding it from four house mix sends. Anyway, the machine is running well been maintaining it by the book all these years but all of a sudden there's an audio squeal (so far) on pre recorded tapes that were done on a "stereo" machine! If I retract the tape tension arm and let the tape run across the heads toward the capstan and pinch roller it disappears. I'm stumped, did the tape tension arm go out of alignment? I'm by no means an experienced engineer but somebody must know what the heck!