Goodmans Triaxiom 212c scratchy sound

I'd like to know what might cause an intermittant light scratchy sound with a Goodmans Triaxiom 212c, whether it can be easily rectified by careful cleaning or is it an expensive repair.
Could be a rubbing voice coil.
Like Twl said, you probably need to re-align the voice coil so that it doesn't touch the side (that's what made it sound scratchy especially at higher volume.)
ditto, above. If so, it's not the easiest job and thereby relatively costly.
Thanks everyone for your conributions to the diagnosis.
rgds, avdb