This is how it should be working. It should HUM with ignition on and engine not running. Replacing the water pump requires the removal of everything upstream of the intake valves. SO, more than likely, you have loosened up a vacuum line or something. Check everywhere very carefully. -Brandon > Ever since completing my water pump replacement project, I have had a > rough idle problem, mostly when the engine is cold > . > I am still working through the obvious possibilities, but in the > process of doing so I noticed that > when the ignition is on but the engine is not running, there is a > soft continuous hum coming from the idle speed regulator (this is > *not* the buzz from the frequency valve). I have never noticed this > before. Is this normal, or could it be related to my problem? >