Unnerving hissing/scraping sound from the engine bay.

[Coast2Coast]

I bought a 99 4Runner Limited a few weeks back. On the drive home after I picked it up, idling at stop lights I realized I could hear this hissing/scraping/somewhat rattling noise up front. It's a constant noise that becomes inaudible when you start to rev the engine. You can just barely hear it when idling. When I open the hood it sounds like it's coming straight from the engine itself.

I initially thought that the transfer case was dry, but then I realized that the transfer case was behind the driver while sitting in the truck so it couldn't be that. There is a big round hole cut in the air box, which may be causing extra noises, I'm not sure. The power steering pump seems to be on the outs because it steers hard intermittently when parking, and the belt squeals when you reach full lock in each direction. Could that make a noise other than the typical power steering whine you hear on old domestics?

Otherwise the truck seems to work great, power is good, idles fine, etc. The engine light came on last week but I checked and it was just an evap system code (P0440 I think) and it hasn't come back since I cleared it. Maybe there's a large vacuum leak somewhere? Any ideas on what might make such a noise? Should I start looking for an engine? I haven't looked into it much since it's a few degrees below freezing on a warm day where I am, and I have on street parking where I live now...

 

[BlackCat914]

My alternator moans at idle, because it's on the way out. Take the business end of a long screwdriver and put on on your accessories. With the engine running, place your ear on the handle. The screwdriver will channel noise and let you know which accessory is making all the racket.