X5d rhythmic pump sound at idle?

[XXX555]

Not the engine and a/c off, there is a sound in front of the dash like a pump circulating every second, not a click or clack, more like a hummmm. Did not hear it on my 335i or anyother vehicle.

Reproducible, now that I know what to listen for at idle. Truck has been near perfect otherwise....except that very high pitched whine using the ipod external music through the iDrive system...