Typical. Just had a rear N/S wheel bearing teplaced on my A4 avant quattro prior to going on holiday and because my ears have been tuned to the tell tale whine of a bad bearing I have heard another noise. Currently on holiday on the west coast, and coming back from the beach I can hear what can only be described as a 'wa wa wa' sound. It's quite a faint noise, but its louder if you're driving next to buildings as the noise seems to be exaggerated. The rear diff is dry, no signs of leaks. The rear diff gear oil was changed at 115k. Currently at 146k. Any tell tale signs of a rear diff on its way out? Would it be worthwhile changing the oil again? Any guides for identifying if there is an issue with the rear diff? Is it worth raising rear of car - spin wheels both ways, any tell tale sounds to listen for?