99 Limited chirping sound

I will do my best to describe this intermittent problem.

I have noticed a chirping sound that seems to be coming from the rear of the truck, almost certainly the right rear, however I cannot necisarily isolate it to the wheel area. The chirping sounds like a small bird's chirping. The only other sound I can compare it to is the sound my Tacoma's a/c vent fan made for a while.

Now for the instances of occurence:

It is most noticable at low speeds when you are, for instance, coasting in to a parking place or driving through a residential neighborhood. Also it gets louder and faster if you barely give it a little gas, just enough gas to keep rolling on a level surface. It seems to be linked to either engine, tire, or drive shaft RPM, but I can't be certain as it's hard to pinpoint because it only happens when the truck is moving. I have tried various things to isolate the problem; A/C on/off, Heater on/off, 4wd, 2wd, all gears, reverse, parking brake on/off, during braking, over bumbs, nothing seems to affect the chiping. Also, as you accelerate it sounds like the noise goes away but the sorta morphs into a new noise at highway speeds, an even harder to explain noise, a little more rough and metalic mabye but it's hard to tell from the road noise.

The noise gets louder and louder until the neighbors can hear it as I pull up to my house and is kinda embarassing, then it won't do it the next day, and a month goes by and then boom, same noise back. Back for a day or so and then gone and so on. If I didn't know better I would say the occurences were in time with some of the local weather changes (Ausitn, TX).

Airplanes are my thing, not cars but I'm not bad with a wrench. Any advice is better than nothing at this point. It is just not a noise I would expect from that area of a truck.

Thanks,

Ty

If it goes away when you apply your brakes, I'd be tempted to say that it's one of your rear shoes rubbing. Maybe the return spring has lost it's tension or there is insufficient brake grease on some part of the mechanism. Your parking brake may not be releasing all the way either because of bad adjustment or because of a sticking pivot on the wheel backing plate.

If you don't see an effect when you brake, then perhaps it is something foreign in your wheel well, like a branch. or something wrapped around your drive shaft. Maybe your driveshaft needs to be greased.

it doesn't go away with break application both normal and parking brake. I will double check the inside of the wheel and drive shaft but upon initial inspection I did not notice anything out of place or on the drive shaft. I had a clunking noise when breaking that I posted here in sept that turned out to be the splines. At that time (4 months ago) I greased everything on the drive train, all the joints and splines. I wouldn't think they would need grease so soon again, would they? Could it be something to do with a wheel bearing? I have no idea how the rear end is put togather so i'm just throwing stuff out there.

Thanks for the speedy reply

Ty

You think you're operating blind, I can't even hear the noise. :)

I think your best bet is to determine the frequency of the noise and tie it to driveshaft rotation frequency or tire rotation frequency or eliminate both of them. Odds are one of them is exactly the same frequency as your noise. The driveshaft frequency should be about 4 times the wheel rotation frequency.

Also, is the frequency dependent on the gear your in? If so, it is a transmission thing.

If you drive 10 mph, the tire rotation frequency would be around 1.8 revolutions per second. The driveshaft rotation frequency would be around 6.7 rotations per second.

good idea Brian, I'll give it a shot, thanks.

Ty