Hi there, first post here. Got myself a lovely 644 recently and been having all sorts of fun with it. One thing that is puzzling me greatly though, is that there appears to be discrepancies between different cassette tapes used. When I turned it on first to test the unit, I tried recording on all tracks 1-4 (using a BASF Record ii Chrome cassette), and it appeared that track 3 wasn't working at all. BUT, when I used a different cassette (same brand/model), all four tracks worked perfectly. Having tested 5 other unused cassettes (EMTEC CE ii), I found that similar anomalies occurred, where 3 of the 4 tracks would be perfect and one would be of significantly lower fidelity, noisier and lower in level than the others. The dodgy track varies from tape to tape. I really can't get my head around this, as on one of the cassettes tested all tracks work perfectly. Any help would be much appreciated, I absolutely love this machine!