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Just found it on opposed forces. Dynamic damper . Need to find out what it does . Although judging by the state of them they probably do nothing
Service Bulletin #03-55-05
A countermeasure has been made to address noise coming from the rear differential area. The noise may make a high frequency "Hoo" (Harmonic) noise and is most noticeable with little to no throttle application (coasting or deceleration). The peak of the noise occurs at 63 mph (100 km/h). The noise may occur in any gear or engine speed; however it is most noticeable in 4th gear or 5th gear. Dynamic dampers were added to the rear differential member to eliminate the noise.