2008 loud vibration/rapping noise

Almost always after going up a long hill my 2008 forrester will make a noisy vibration/rapping noise. The noise continues untill either I slow down or the road levels out. I bought this car new and it seems to be getting worse. The dealer cannot find the problem.
My extended warrentee is almost up and I want this car "fixed". The service manager rode with me and heard the noise so hopefully it can be fixed.

Anybody else have this problem?

Any suggestions?

Thanks!