As Nige said, picture speak a thousand words, so we NEED pics
These axles are not as easy as just listening out. There could be numerous reasons for a noise, gears worn (high milage), carrier or axle bearings going, or if the pinion seal is leaking (common problem) it could be the pinion bearings. All bar the axle/wheel bearings mean the axle needs stripping. However, sometimes even a nice oil change can help wonders. Some good redline 75w90 diff oil would be great. I have an old axle I used to drag race with where the pinion bearing is not in the best shape but it doesn't make a murmer. Maybe i'm over picky and checking all the settings? Just rebuilding a high gear axle now for the strip and was happy/sad all at the same time that the bearings I took out were totally fine and not pitted etc.
Not really big jobs need doing with your car to get it in great shape, but the market isn't brilliant at the moment. 2K seems a fair price with car as it is, but if the body work etc in in very good nick and the car doesn't show its milage then that will obviously push it up a bit, maybe you could get upto the 3K mark, depends on how fast a sale you want etc.
PM me if you need anymore help on the issue.
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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)