In Reply to: What is that #$@*! Humming Noise!? posted by Kirk on October 06, 1999 at 10:41:03:
1. I am assuming that your car is 96 or newer. Mine is a 98 and every time I start it that noise comes in.
2. Basically all it is is a fan that dilutes the cold engine exhaust gases or whenever the O2 sensor tells it to. Emissions control basically. By flushing more air with the exhaust before the cat you reduce NOx emissions drastically as well as CO emissions.
3. You can see the snorkel it uses behind the passenger headlamp and the pump itself (if I recall correctly) is mounted to the firewall or near there.
4. You can see its plumbing to the header end if you look carefully.
Thats at least what I noticed when I stuck my face under the hood.
Finally, if you hear it when the car has been run for a while, it could be the radiator fan, but I think you can tell the difference (not high pitched).