I am hearing a fairly loud buzzing/whirring noise when I decelerate at speeds above 25 mph. The noise stops as soon as I touch the gas. At highway speed, if I put it in neutral (auto trans), the noise is still evident as the rpm's lower and then disappears at idle.
Transmission fluid level is good and so is the color. The transmission shifts up and down without any hesitation. The engine runs perfectly and fuel economy has not changed.
The Ford dealer had it on the ramp and detected no leaks. The problem started suddenly as I was driving on a freeway in very cold weather (-10F) and I'm wondering if something froze the previous evening even though I had the block heater plugged in.
Anyone experienced the same problem?

 

You might want to check the intake system. If there is a loose clamp or connection in the intake system this might explain why you get the buzzing noise since the throttle butterfly is closed on decel and you can stop it as soon as you open the butterfly a little. Also a loose or questionable vacuum hose could be a cause.