I've got this sound coming from somewhere, like a whining. think of a playing a wine glass, but deeper with about the same frequency. I really don't know how to explain it. It happens sometimes at random rpms, only when the truck is moving, it does not get louder or softer when I accelerate, I cant hear it above 20 mph. It is always the same pitch. It happens sometimes and not other times all under different conditions. and of course never when a technician is able to come along to hear the problem. Any insights? Also it doesn't seem to effect the driveabilaty of the truck at all.

 

Its got all you stumped too? Or have I not explained it well enough?

 

174K? Have you checked your Ujoints? I noticed mine making a barely noticeable hum on a stretch of new, smooth asphalt. I have a big trip coming up so I decided to drop the rear driveshaft and my rear ujoint was shot (for the third time in 247K). I can't tell they are going bad with a visual. I have seen it 3 times. Joint looks and feels ok, when it is dropped, you can immediately tell it is bad. Good luck and let us know!

 

Did you just have any work done? Possible front brakes or heat shield rubbing on rotor. Does noise go away if you hit the brakes? Possible hydraulic noise from P/S hose or hydroboost. I have heard coolant going threw the heater core making noises also. I have even heard the water pump and alt making high pitched noises.

 

I have been paying more attention to it. It is hard to test it to wee what it does and when, when you are in traffic. noise does go away when I step on the brakes. I recently changed the injectors, nothing in the engine bay is making any noises outside of normal. you would think u joints would make noise all the time. this only happens some of the time, and always at the same pitch and speed does not change the noise at all. sometimes it is really loud and sometime you really have to listen for it. P/S is starting to go, pump squeals when I turn, once in a while. could that be it?

 

I would go after the turbo hose clamps, make sure they are all tight and that the hose is all the way up where it's supposed to be. They will make very loud noise when under acceleration when you have max boost pressure. ALso check the intake make sure the gaskets aren't leaking at the heater grid since you said you did injectors recently.

 

how do you go about checking the gaskets? Is there a torque setting for the boost tube clamps? I never do hear it at almost full throttle

 

See if the gastket have blown out also check around the exhaust manifold for any gastkets that have slid out of position and if any soot around the head where manifold attaches. Check the exhaust bolts for proper torque. Make sure no bolts are missing in the intake if they are you will loose boost pressure and will make a whistle noise, these bolt holes go completely thru the intake.