2007 BMW 530xi with pong noise in front when hits bumps it magnifies. 1 dealer said differential (replaced front differential & still same problem). Also replaced front left wheel bearing (still same problem). Swapped wheels & tires w/another 5-series & still heard same pong-noise (sounds like a rubber ball in a tin can noise). 2nd Dealer suggested swap for better Michelin Pilot tires which are softer & better insulated tires which are known for noise reductions. Will have these swapped on 8/19/2010 at dealer for no charge. Any suggestions?