Engine Noise--2000 MPV ES

When I drive and usually at idle there is a noise that sounds like a howl-vacuum leak--like someone holding a note like singing. Seems to be quite loud at idle and just had it inspected and no-one said anything bad. Seems like it could be large but go's away upon acceleration. Its just annoying . If I get some leads from others I can check it out. Brake booster came to mind.

Its the IAC ( idle air control) valve . I found out from an MPV forum. They sound like many different things but a low fog-horn is the best.