How do we debug a scratchy sound?
We can isolate it with the balance to a single speaker.
But is it the speaker? Or something else?


Interchange the wires at the speakers - you'll prove that it's the
speaker and not the stereo or wiring.
Pull out the bad speaker & look for a tiny tear - try fixing it -
http://www.300guitars.com/300s-tips/...speaker-cones/
or shop for a replacement.
John T.


Keep it simple - introducing more variables - such as a different
third speaker and its wiring .. etc just confuses the issue.
... especially when a simple and straight-forward trouble-shooting
method is available.
John T.