[quote="drakula63"]Thanks folks.
Yeah, I guess it could be 'print through' as the tape hasn't been played for about 20 years. I am still of the view that by erasing the unwanted tracks this might provide a solution./quote]
Whoah!
Don't erase anything!
There'll be a solution which doesn't involve destruction.
As described by Ulrich above, the problem is that tapes recorded on older formats are backwards compatible with replay on newer machines, eg:
(a) full track will pay OK-ish on half (twin) track
(b) twin track will play OK-ish on 4-track
(c) [even] full-track will play back well on a 4-track machine,
...but not the other way round. Tapes recorded on later formats will not play back satisfactorily on older formats with a lower number of tracks.
I bet your tape will play fine on a 4-track reel to reel recorder (whether mono or stereo).