Engine Noise on 1999 Porsche Boxster

My 1999 Boxster (70k miles) has recently become louder while driving. It starts to get loud once the car gets up over approx 25 mph. At higher speeds if I place the engine in neutral the noise does not diminish. It is only when I get below 30 does the sound begin to go away. Any ideas? Thanks, Brad

Asked by for the 1999 Porsche Boxster
Yes, I would check the final drive bearings in the transaxle, a pretty common issue as the car gets some miles, like over 100k. There will be a constant low sound from about 30 mph and will be more noticeable at freeway speeds, when you put the car in neutral, the final drive bearings are still turning, as the final drive connects the transmission to the drive axles, so the noise will still be there.
Thank you very much for your help. Do you know how much it will costbto fix ? And do you know of a good Porsche mechanic in San Diego?