I have a 94 ext. cab 4 cylinder 5-speed p/u with 165,000 miles. When I am on the highway 60 mph or above I hear a roaring noise from under the truck, but it is not a constant noise. The truck does not drive different when I hear the noise not do the rpm's change. As far as i can tell the clutch is good. Everything is stock except for a K & N air filter. Any one else every come across this before?

Have ya checked the running gear fluids? sometimes the rear ends will growl before taking a dump!!!:cry:

I had the truck in a shop last year and they checked the fluids in the transmission and the rear end and since then I have not spotted any leakage from either.

I would check them myself and do not trust anyone to due quality maintenance because not too many maintainers that do quality work!

I'm wondering if it could be the fan clutch. how would you test it?

So with your 5 speed the stick is on the floor; right? Check to see if the boot is loose and allowing air and noise into the cab.:cool:

the shift boot is on. about two weeks ago the timing chain guide went out so i went and bought a timing chain kit and a new water pump from toyota and had it replaced. i had been reading about the guides wearing out and was kind of expecting it with the mileage i had on the truck. only thing now is i hear valves? clattering when i'm going up a bridge(might bring back to mechanic and check the timing). still runs good and gas mileage still 22 all around.

check the rear wheel bearings. It is very easy to pull the axles out and a machine shop will charge about $30 to press new bearings for you.