Humming noise changes with rpm

[mechjames]

Today is the first time i've started my explorer in about two weeks. Recently there was a little bit of humming and vibration at about 1800-2400 rpm. It would quiet down when it got warm after driving.

Now, I start it up, humming noise is a lot louder (like the synchro's in a manual transmission when they're worn), but my truck is an automatic. Its loud enough, I could hear it inside my house while parked outside the window. I noticed it because it doesn't sound the way it used to, which was just stock exhaust noise while idling.

What could this be? This does get louder and change in pitch the faster the rpms are from idle speed. I'm worried it might be transmission input shaft bearing (If the A4LD has one, i'm not sure, don't know transmissions too well), but could some engine bearings make that noise too? Vibration and Humming?

 

[Douglas70]

My 02 Explorer is doing the same thing. Have you figured it out?

 

[Turdle]

Could it be the power steering pump?

 

[kona_mtb]

How does the rpm sit well you are idling? Is it steady or jumpy? Just wondering because on my dads car (not explorer however) he would get a humming noise that first started at select rpm then after about 3 months became steady and then his timing chain snapped. The garage told him that was the noise. I ask about the rpm because that was another symptom, a jumpy rpm.

 

[mechjames]

Yes, I did. After a couple of months, I took the drivebelt off, and checked the play in all the accessories. My water pump had play in it, and the fan/clutch was shaking/vibrating because of so much play. I changed the water pump and it went away.