Loud "Hum" from under the hood!

[JennyLeeCox]

Morning....I hope this is the correct pace to post my question.

I have a 1999 Ford, Explorer....Recently it has been making this loud humming sound when I am slowing down or stopped. It never does it when I am driving at a decent speed. I had a friend look under the hood...he said it was coming from somewhere near the air filter....We changed the air filter...cleaned out the box it sites in, cleaned the air flow sensor....we also changed transmission fluid and filter because someone said it could be transmission belts. The big serpentine belt looks good and this phantom noise continues...someone else said it could be the fan clutch.....anyone had similar issues or have any ideas as too what this crazy noise could be???

 

[Jstcruz]

I had an air bypass valve humming real bad one time.. its kinda loud and would be easy to find tho. does it hum at idle or only when you are on the breaks for the most part?

 

[swshawaii]

http://www.explorerforum.com/forums/showthread.php?t=84220&highlight=clean+iac

 

[barenfang]

IAC Valve

Pretty sure it is the IAC valve. You can clean as the above post indicates or go to Rockauto.com, order the part($46), and replace. It is really easy to replace. I had the same issue twice in the time I have owned my Explorer.

 

[DjDom]

Very common problem in Second Gens.
Mine's been doing it for years, no ill effect. Except people look at you funny when you pull up to a red light and start humming.