Loud Humming Noise between 40mph and 50mph
 

Today I bought a 2000 911 Convertible Automatic Transmission with 25k miles and discovered a loud humming noise coming from the rear that begins every time I hit 40 mph and stops after 50 mph. It is much louder than the engine or muffler sound. It also stops as soon as I release the gas pedal or place the car on cruise control. So it only happens when I am accelerating between 40 mph and 50 mph. Any and all of your suggestions will be greatly appreciated.

I drove with a technician today and he said that the sound is normal for an automatic on this model and the Boxter. He said it was RPM related and that it was air traveling through manifold. Your thoughts?

So webmartinez, how did this progress? Was it really RPM related? I have the same humming sound issue with my 99 911 996. I was contemplating whether this is caused by worn out rear wheel bearings..? But since the humming only occurs when the gas pedal is pressed or when you accelarate, maybe its coming from a low level tranny AT fluid/oil..?