Soundtrax recording problem



I’m using Nero Soundtrax version to record songs from tape deck as wav. files.
Seems to be working just fine and then the sound goes breaks up and goes warbled, as if the tape is crinkled or something…this is not the case.
I’m using a Teac 32-2B 2 track mastering deck…deck and tapes are in prime working order. My cassette deck does it too.
Probably a simple solution, but this simple guy doesn’t know what it is.
Appreciate any help, Thanks