2000 Ford Expedition - Intake Noise that sounds like Exhaust Leak
 

Any mechanics out there who can tell me what this noise is:
Background:

1. Noise seems to come from the air intake. When I take the intake off, I can hear the noise through the intake tube.

2. Noise is RPM dependent: hear it at 1000 rpm, but not lower RPMs

3. Noise is reproduceable with RPM around 1000

4. Noise started after I replaced the IAC valve and TPS. I'm wondering if a bad gasket on the IAC valve could cause this noise?

Try removing the air intake and replace it with the stock one and see if it goes away.

Hmm . . . that K&N Cold Air Intake has been on there for many years without a problem. I did recently remove and re-install it, though. So, although I don't think the stock vs K&N is the issue, maybe an air leak around one of the rubber connectors could cause this?

Solved the problem. It was the new IAC that I purchased from AutoZone. It was creating the problem. I put the old one back on, and the problem immediately went away. The new part looked exactly like the old part except for 1 minor difference, the electrical connection was clocked 90 degrees counter-clockwise. The connector fit correctly, but was clocked differently from the factory part.

Glad you got it fixed. :)