Sounds are dificult to diagnose with out hearing them, but you might want to look into your rear end. It's either that or the trans. Narrowing it down to which bearing in the rear is wasted is probably the next step.
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1988 Mustang GT
11.8 @ 123 (7/14/01)
1992 BadAzz Wrangler
1993 Explorer
See my car at:
www.mustangworks.com/cgi-bin/moi-display.cgi?179