Okay, please don't jump all over my post for lack of information. I'm just trying to get some clues on a very strange noise from the engine area. This noise only happens "now and then", but is really loud. The only way I can describe it is like a Fuel Pump x10 or and electric motor if you stalled it. Almost a lound Humming sound. I know this isn't much, but what could make sounds like that under the hood and then go away after about 30 seconds (EGR valve?, it doesn't seem like it would be a fan because it's not while the car is really warm). I haven't had the chance to get out and pop the hood while it happens, it always seems to be somewhere I can't pull over.

 

Airpump below front left headlight?

 

does it do it more as you corner? and when you let off the throttle? if so it could very well be your harmonic balancer, the sound your describing is exactly what mine sounded like took forever to find but thats what it was

 

You might be on to something

 

Are we talking about the smog pump? If so, what controls when it comes on and off? I'm going to try to get into this more this weekend. Anything else under the hood that can make this type of noise? Thanks for suggestions.

 

Now and when? Under acceleration? De-celeration? Get the stick in neutral - still does it? While braking? Sound increase as speed increases?

 

Okay, finally got the sound to come on while I could stop and look. Though it still didn't help me much. I popped the hood and still couldn't make out exactly where is was coming from, but it's really loud.It "seemed" to becoming from mid engine, like the manifold area......again, I could make it out for sure.The sound only happens, maybe once a ride or maybe less. It doesnt' seem to matter if the car is high or low idle, moving or in the driveway when it happens. As soon as I rev the gas, it stops and goes away. I know I'm not givingmuch info here, but it's the best I have for now.

 

Get the belt off of the belt tensioner. Feel the tensioner pulley wheel for lateral movement (not in line with the belt, but like at 9:00 and 3:00, and see if you can go back and forth with it).

Is the sound like a combo rattle/vibration?

 

HMMMMM........you might be onto something, I was just watching the idler pully the other day and wondered if it's supposed to look as worn (sloppy) as it is. I will check it out today and post back. Thanks