Got a new Cannondale Mountain Tandem 2006 in April 2006.
Over the past 16 months or more have been annoyed by this phantom shush shush pause shush shush noise (pardon the audio attempt) that only comes up after at least half an hour of fairly hard riding and only when pedalling, the more power applied the louder it gets. Embarrassing. Clearly audible to passing or passed cyclists. Appears to be coming from around the back bottom bracket or futher back, perhaps the rear hub. It is not the disc brakes
We have checked pedals, and changed bottom brackets, cleaned the cassette and oiled the rear hub and greased the eccentric, tightened the cranks. At times it appears to be in sinc with the right leg down thrust. It is driving us nuts.
The bike shop has also not been able to isolate it yet.
The rear hub is the only component that has not been fully checked yet.
Any body come across this?? Many thanks