I had trouble with maxell hi-8 tapes in a sony camera. In my case, brand new tape would wobble over the heads completely screwing up audio and video. Ruined some great shots intended for stock footage and prompted a costly reshoot! Just like you, I put in some sony tape on the next go round and voila' clean audio and video signals.
I don't necessarily hold on the 'brand for brand' line as I've used panasonic pro tape in sony's, canon's and now JVC cameras with zero problems. I think it's as 'Cat suggested, just get quality tape. I do agree with finding a quality brand you like and rolling with that.
It's been a while since I used Hi-8 though I do have a working one available. Sony, Fujifilm and Maxell seem to be the only manufacturers left making Hi-8 tape. In your case, I'd stick with sony consumer grade at $3 a tape and use the pro 120 at $7.50 for recording finished work over an hour (and less than two) for archiving or submission for television broadcast.
In the meantime, run a cleaner tape over your heads as dirty heads may be part of the problem.