Originally Posted by showtaper

If it really is from a cassette, the problem may be the soundcard used.

Many inexpensive or onboard cards create artifacts in the audible range.
Can be internal clock interference or other induced noise as well. Cheap
cables used between the deck and computer may be poorly shielded and
picking up stray noise also.

You can see this easily by capturing from a blank tape. There is no inherent
"stripe" in a cassette recording.

Hundreds of ways to get noise into an otherwise decent signal.......