Another rousing game of "Name that sound"...
 

This is on a 2000 4Runner, 3.4, 5 speed, 4WD...

Getting an odd sound at low speed. It sounds like, what I can best describe as, a handful of sand thrown into the motor or tranny....kind of a grinding noise. Happens at about 1200 RPM till about 1400-ish while under acceleration, then disappears above 1400 completely. Usually notice it mostly in parking lots in 1st and 2nd or in slow speed traffic.

Can't really pinpoint if it's coming from the motor or the tranny. Seems to be more pronounced after long periods on the highway. Shifts and drives fine but it seems to be getting louder as the miles rack up.

Any ideas?

This sounds great. I guess...... the thrust diverter is irraticly modulating. just kidding. does it do it in first and second or only in one gear. if you are decelerating down it goes away. lets say its in first gear and you start to drive, you get to 1200 rpm noise starts, you continue to accel to 1300 noise still present, then you release throttle noise goes away, then you reapply throttle noise returns, untill you cross 1400 rpm. if you repeat this process in 2nd gear, noise is the same? if you repeat in 3rd gear noise is not present?

I notice it the most in the 1st to 2nd gear change at slow speeds. If you release the throttle while in the 1200-1400 RPM band, the noise goes away...only happens under acceleration. Like I said, it seems to be most pronounced in the 1st to 2nd change but it does it ever so slightly in other gears also which is why I'm thinking it might be in the transmission.

Going to see if I can replicate the problem in an audio file... it's almost sort of a dieseling noise like when you lug a gas engine down really low. Not really sure how to describe it other than it sounds like it has a handful of sand thrown into the mix somewhere.

It does almost sound like your putting too much load on the engine at too low RPM. Both of my trucks make a similar sound from what you've described. My trucks make that sound when I start out at too low RPM or when I try to accelerate when in 1st gear at around 1000 to 1200. From what you've described (unless it's a really really loud low rhaspy tone) it sounds normal, as least in my eyes, esspecially if the sound is only present in the super low RPM ranges under acceleration but not evident under any other situations.

I know the transfer case in my old 85 would make that same sound, but I never stressed it. I probably would on something I didn't beat though

Well, I don't think I would call it "normal" but it certainly doesn't appear to be anything to worry about... just yet.

Thinking it's just one of those things I'm going to have to wait for something to break as I really don't want to start tearing things apart guessing what it is. In the mean time, guess I'll just turn the stereo up a little louder... :wrench: