Start at the air filter and check for any cracks and loose fitting, check for vacuum leaks at the throttle body, start here.
July, 25, 2011 AT 12:02 PM
Took off filter and intake pipe. Noise seems to be coming from air chamber going to the IAC valve. When power is removed from IAC valve noise stops but idle goes down real low. Could it be electrical? I removed throttle body cleaned it real good and replaced gasket. Going to get replace valve again to see if I got a faulty one.
July, 25, 2011 AT 1:29 PM
Do that and report back results.
August, 8, 2011 AT 12:43 PM
Ok! Finally was able to work on the car. I replaced the IAC valve with another one also cleaned the MAF sensor(hot wires are not broken)and the EGR valve. Checked vacuum lines found small tare, but did not seam to effect it. Sound is still loud at start up then mufles down after car is warmmed up, but gets loud when RPM's go up. When RPM's are coming down engine idles rought. What else can I check?
October, 7, 2012 AT 7:48 AM
I have almost the exact identical problem. Tried 3 different IACs did everything you've done and is still howling.
Description: As soon as the car is started the noise starts and then after about 30 seconds it will tone down. I notice when im driving around 5 mph and slowly press on the gas pedal it will go away and then reoccur once I get to 20 + mph. I'm stumped, my mechanics are stumped! Is there anyone out there that has an idea of what this may be?