Tone from under the hood

[redhat]

I hear an abnormal tone - sounds like high pitched horn - although not that load. Does not happen all the time and does not seem to be temperature related. Usually happens at low RPM. It sounds (with hood up) to be coming from the air intake, just above the filter. I wonder if there is a vacuum controlled valve or something that might be causing this. Sounds vacuum related?

Anyone heard a similar noise?

thanks.

 

[Alec]

It's probably your IAC (idle air control valve) getting stuck. I suggest using the search engine on this site to look for related threads. Good luck!