83Daytona500

driving along one day and i heard a rubbing noise... sounded like a tire rubbing on a plastic piece and i would get higher pitched as i accelerated, i looked and looked and i couldnt find the problem finally my buddy was driving along beside me and told me the thought i was the rear differential... so i changed the fluid... in doing so my gears looked fine... no sign of any rubbing or markings on the teeth... but of course you cant see everything from the gear box... so i put everything back together refilled it with fluid and hoped to *** that the noise would go away.. i didnt and thats why im writting WTF is the problem