Ideas on whining noise coming up in the cab

[Piratehunter]

truck - ’97 k2500 454 nv4500

just started hearing this in the cab. Whining noise, that sounds like coming from up from under the dash area, but not certain the source. Steady increase in sound level as I rev through the gears, drops off at pedal lift for shift, and picks up on acceleration again, most noticeable 1500-2500 rpm, the noise is still there above 2500 rpm, but gets drowned out by road noise. Same whine when not moving and reving it up in that range.

sounds similar to the whine you hear of a big dump truck size truck going through the gears, also reminds me of the noise of a flex fan blade. Can’t really isolate it by going under the truck or under the hood with someone operating the throttle. I’m very hard of hearing, but this noise is annoying.

going to remove the serpentine belt to eliminate all the pulleys tomorrow. This might be a hard one for a near deaf guy to figure out.

 

[1998_K1500_Sub]

I've heard water pumps on some vehicles whine quite audibly.

I once had an alternator emit a very audible whine that varied with engine RPM.

At the time I didn't know that the alternator was the whine source, but eventually the alternator completely died and with that the whine went away. Then I knew.

I was young.

I assume a diode(s) must have failed and the current imbalance in the stater caused audible vibration of the windings. Sometime thereafter, it simply stopped charging.

 

[Nad_Yvalhosert]

If you hear it when parked, think engine.
A mechanics stethoscope will help diag a growling bearing on the serpentine system.
Removing the belt and spinning them by hand will give you a feel if you're ears deceive you.

 

[Schurkey]

Any chance you're hearing alternator whine through the radio? I don't know about these vehicles, but in The Olden Days, there'd be a capacitor or three connected to the ignition coil, and the alternator, to keep electrical noise from radiating into the radio. The alternator made a whine, the ignition coil was more "static" or a buzz.

Failed or missing capacitor(s) were the cause.

 

[Keeper]

hydroboost whine

 

[Piratehunter]

Any chance you're hearing alternator whine through the radio? I don't know about these vehicles, but in The Olden Days, there'd be a capacitor or three connected to the ignition coil, and the alternator, to keep electrical noise from radiating into the radio. The alternator made a whine, the ignition coil was more "static" or a buzz.

Failed or missing capacitor(s) were the cause.

It's not through the radio, radio is not on. too cold and windy out today to do much on it Was able to put a stethoscope to the belt driven components for a few minute,but didn’t have a helper to rev it up. PS pump definitely louder than the others. snowing tonight and tomorrow, may not be able to diagnose more till Saturday

 

[Piratehunter]

Released the belt today, noise is not heard. All pulleys spun good. A little wobble on the tensioner and idler pulleys. Put the belt back on and had a friend rev it up while I listened at all points with stethoscope. Tensioner pulley sound amped up when reved up. Going to replace both of those pulleys Sunday. Hope that is it. Elk hunting the next week, backcountry breakdowns I don’t like.

 

[454cid]

Released the belt today, noise is not heard. All pulleys spun good. A little wobble on the tensioner and idler pulleys. Put the belt back on and had a friend rev it up while I listened at all points with stethoscope. Tensioner pulley sound amped up when reved up. Going to replace both of those pulleys Sunday. Hope that is it. Elk hunting the next week, backcountry breakdowns I don’t like.

Good job, for tracking that down. Years ago, when I had a whining noise, I thought for sure it was my alternator bearings. I ordered a new (maybe rebuilt) AC Delco alternator, and installed it, only to still have a whining noise. Another week or two, the idler pulley made itself obvious as the real source of the noise. For some reason my original pulley only had a brass (bronze?) busing, not a bearing.

I still have my original and perfectly good alternator in the box, from its replacement, sitting on a shelf. The 2nd alternator has many more miles than the original now.