The most likely cause is that the cassette play heads are worn or out of alignment, causing phase-discrepancies.
It is likely affecting the entire recording, but is most noticeable at frequencies where the phase-cancellation is worst - where the higher & longer notes will show it up.
You'd be unlikely to spot it happening on the bass, as the head alignment would have to be much worse to spot it, by which time the guitar would become almost unlistenable. Drums are less likely to show it, as they are of short duration.
If you're feeling brave, you can attempt to realign the heads yourself. I wouldn't recommend it if you only hear the problem on one cassette, or if the player is actually worth more than a few pounds/dollars/shekels.
There will be a small screw just under the play head, only accessible when the unit is in play, & sometimes only with the cover off.
A slight twist left or right, aiming for where the sound is brightest, will cure it.
This is not a perfect solution & don't attempt it if the gear is worth anything, but it's how an old-school sound engineer [me] would do it… though I'd have a meter to measure it, for all but a quick playback tweak ;-)