Engine/Transmission (1998.5 - 2002) High pitch "whirrr" at 8lbs of boost:

[SWEdholm]

Need some of your ideas; Recently, and in the last few days pulling a new 5er, shifting through the gears, under load I am getting what I can only call a high pitch "whirr" usually going up through 8 lbs of boost and stopping at about 10 lbs. The sound seems to be comming from the drivers side under the hood. The only thing I can tell that seems to coincide is the boost. Did all the checking under the hood for the obvious and found no loose/cracked/broken hoses. The only thing mech. recently is a replaced o-ring in the vacuum pump, resultant of a oil leak, (about 750 miles ago) no leak and seemingly good vacuum. This sound does not happen just while towing a load, just normal driving results in the same. What do you think??

 

[B.G. Smith]

Mine used to do the whirr thing when the air filter started to get dirty. I also had a mystery noise that my wife would hear when towing and the boost got above 10 pounds, turned out to be a loose connection on the back of my boost gauge. bg