Cleaned the plates with wet n dry? That'd make the diff action rough. You don't want to be doing that.... years gone by I used to polish up diff plates on a flat tile with a cutting compound for hours... sad I know.
If you hear a 'bark' rather than a 'squeel' thats the diff slipping slightly (if it slips lots it'll just squeel though). If it squeels, thats the slipper clutch and that is okay. If any doubt, take gear cover off, hold a wheel and thumb on spur - turn the other wheel so something has to slip - the slipper nut should always turn otherwise its the diff slipping.
Any doubts, take it to a shop or a club and get a second opinion.. its far easier to diagnose & solve hands-on, rather than like this on a forum
