If the tapes you recorded work OK in another machine then there is only one possible thing that you can try, that being to try cleaning the tape head, as if its heavily contaminated with flint like deposits that will give the effect you witness. I always recommend that in cases like you mention the only real effective way of cleaning the head is by using the "wet" method, as these dry cleaning cassettes not only put the head in danger of being damaged by over cleaning but they aren't always very effective either. However unfortunately because you have restricted your e-mail address it excludes sending the wet cleaning info on to you, as it contains a JPEG for illustration purposes which cannot be sent via this website. I should point out that if head cleaning doesnt cure the problem then its a dismantle job to determine the reason, with the first thing under suspicion being the mode switch.