I have a 98 F-150 with a 4.6. I have started to get a howl from my Air Intake. This only happens at low rpm and does not happen all the time. I have removed the air cleaner while this is happening and it is coming from the intake. Any ideas what this might be?

 

This may or may not be your issue but i've heard of a faulty IAC valve causing a howling noise. If yours has never been changed before it might be worth looking into.

 

I have not checked the IAC. The performance of the truck has not changed in 170K miles. It idles and runs great, just makes a very annoying howling noise at low rpm. Could this still be the IAC