Burning smell from air vents

I've got a 2005 nearing 100k miles. Once in awhile when I turn on the A/c the engine would make a
grinding noise that I assumed was the A/c belt slipping. I never addressed that yet. A couple times
a week now I'm getting a burning smell from my air vents for about a minute then it goes away.
This has happened immediately at cold start up and after driving for some time. I mostly feel like it is the smell of burning rubber, not really oil. And I dont think oil would burn when the engine has just been started. I have noticed some oil seepage along the top passenger side of the engine. But I wiped this clean and not noticed any reappear so I cant tell if the head is leaking or it was just grime and gunk. The belt looks fine, but I'm thinking maybe its loose and the pulley is spinning free and heating it up for a few seconds, then maybe expanding with the heat.
I'm wondering if anyone else has had this experience, and any advice anyone has. Im considering if I should just go ahead and have the belt replaced as the truck is nearing 100k anyway.
Thanks for your help!

 

Just a guess and thats all, maybe alternator windings. Though it may be something else Im not an auto mechanic. The burning rubber smell points me that way. The Ac comp. is just a pump so I doubt it would smell. Oh hell, its hard to sit here and give input. Hopefuly the more knowledgable here will chime in.

 

Maybe it's a tumor...




But really, set your AC so it's pulling only cabin air and see if it does the same. You shouldn't be able to suck in anything from under the hood to start with unless you're belching smoke up and around the fresh air intake for your heater system. A slipping belt etc shouldn't be an issue. If you've got something burning IN the system, you're going to have some problems coming soon.

In general a slipping belt won't make a grinding noise, it will squeal. You have metal slipping against rubber, think the sound a balloon makes when you rub it.

 

Well good news and bad news. I've found the problem. There was some oil seepage along the valve cover on the passenger
side that I was watching for problems. I wiped the oil away and kept an eye on it to reappear. There is an oil leak somewhere along that side of the engine and there are small drops of oil dripping down onto the header pipe resulting in the burning smell. My truck parks on an incline and when I walked back to my truck this morning after forgetting something I could smell the engine outside. When opened the hood the header pipe was smoking and there was some fresh oil dripping off the valve cover bolt nearest the firewall.
Anybody know the torque specs for the valve cover bolts? And would it be a bad idea to put a wrench on there and check the bolts? I dont want to strip anything out. I already tightend the one nearest the firewall. It had a small amount of play in it. The others seemed ok.
Thanks for the help!

 

The only good solution would be to replace the valve cover gasket. Common problem on those plastic covers. Not that frequent on Toyatas, Ford 4 cylinder engine are even more common for such problem.

Oil dripping to hot exhaust manifold can also pose potential fire hazard.... don't take chance. It's not that difficult to replace the gasket on those 4 cylinder engine

Torque on valve gasket bolt/ nut is 80 in.lbf (notice it's NOT ft.lbf)