I get this humming noise when I start the car and it get louder as I drive. This noise goes away at certain RPM's like when I'm in overdrive (lower RPM's). I checked under the hood and listened for the noise,it's comming from around the Power steering pump or alternator. I just don't know witch one it is. Everything checks out to be good so far,no charging problem,no steering problems,fluid is at correct level. I'm baffeled,help!!!

Take the belt off, and see how they spin....or get a stick and listen to each while riunning.

Alternator bearings usually whistle or whine when they go bad...a rumble or low hum would be more in line with a P/S pump....could be the belt tensioner bearings too...does the tensioner arm chatter or jump around while it's running?

I did take belt off,alternator spun freely,power steering spun,but they must have vains to pump hydro.-oil thru lines. I'll tell you what,the noise sounds like a hydrolic presses whine. The lines go across the alternator,and they feel like they a vibrating but it could be the alternator,but that spins freely. I did have to take the pump off to replace the cam position sensor. Also noise is not comming from the tensioner. Thanx

Are you saying the sound appeared after removing the pump?

Just curious, because those lines do hum with the pump turning...if not tightly clamped against something they can resonate pretty loud...make sure the pump mounts are tight and the pump is not running off-plane with the other pulleys....sometimes a spacer or bushing gets dropped and they don't sit straight after...

Did you try putting some pressure on the different parts (alt, pump, lines) and see if the sound changes, just lean down hard on them and see what you get?

If the sound is like a pump under load, the power valve in the pump may be sticking...you could suck some fluid out and try some Seafoam tranny conditioner or something like that in it...

The alt should spin freely, but if too freely with any bearing hiss, it's done