Scary sounding whining noise

[justinburnett]

Sometimes when driving, my 1973 GMC k2500 develops a whining noise. This changes pitch according to RPM. Seems to only happen once it's warmed up a little bit and DOES continue if I stop and put it in park. It is intermittant and so far I haven't been able to get it to do it when I could take it to a shop to have them listen. I've gone so far as 200 miles with no problem, and then the next day have it happen just going to the store. It drives normal, no weird vibrations or loss of power. Checked all fluids and they're good. Honestly sounds almost like a power steering pump when it's low and you lock it to one side. The only thing that I've noticed is different as far as operation goes is one day it did seem to hesitate when I went to take off from a stop sign, but I'm not 100% certain if it really did have a delay or not. Was not making any strange noises at the time. I have checked fluids in engine, trans, all diff cases, transfer case, and PS pump.

All I have done lately (last 4 months) is replace the starter and flexplate, and change the fluids in the transfer case and rear diff.

Please throw some ideas my way that I can check and see if that's what it is. I'm worried about it causing worse problems if I drive it, and I need to from time to time.