2003 4Runner engine noise

My girlfriend has her dads 2003 4Runner for a week (car is for sale, if anyone is interested), and she picked me up for lunch today. Riding in it, I noticed that the engine is groaning. It sounds like it is under load and always accelerating, even if it has been going the same [low] speed for a mile. Revs are right where they are should be. Downshifting makes the revs go up--noise stays the same, just gets correspondingly louder. It isnt' something that screams "something is wrong you're gonna die!", and someone who jumped in it for the first time ever might not notice anything, but it just didn't seem right to me.

Any idea what this might be? It is a V6 with 150k miles, and it drove about 200 miles yesterday apparently making the noise the entire time with no apparent issues.

noise matching road speed, engine rpm or transmission/transfer case speeds - does it need to be moving or under some load to make the noise??? My first instinct would be checking the transfer case fluid. I've noticed on our 2007 4runner that it's well insulated enough that identifying the source of noises gets tricky. I've resorted to mounting a go-pro underneath and driving around to locate noises (i.e. loose heat shield mimicked speed/rotational noises).

oldtin wrote: noise matching road speed, engine rpm or transmission/transfer case speeds - does it need to be moving or under some load to make the noise???

Yes it does. I also just texted her to see if it might have somehow been put into 4wd.

If it doesn't change pitch with engine speed it's almost surely nothing in the engine itself or any of the accessories. Could be some kind of exhaust drone.

Edit: Oh I see you don't get it when stopped. I know my sammy makes a low-pitched gear noise in 4wd, but it has a diffless gear-driven transfer case.

GameboyRMH wrote: If it doesn't change pitch with engine speed it's almost surely nothing in the engine itself or any of the accessories. Could be some kind of exhaust drone. Edit: Oh I see you don't get it when stopped. I know my sammy makes a low-pitched gear noise in 4wd, but it has a diffless gear-driven transfer case.

It does change pitch with engine speed, I apologize if I wasn't clear. Isn't diagnosis over the internet fun? Why did we ever try to do it any other way?

I vote fan clutch.

Check the trans fluid level along with the other levels. You might also take a look at the CV joints while you are at it.
It really doesnt sound motor related; at least from this distance.

Curmudgeon wrote: I vote fan clutch.

+1