Chevrolet Repair: that c30 chev again, tail shaft, horse truck

Question
I wrote once before,and took your advice..so thought i would tell you where we are up to. i have a chevy C30 1977 that i use for a horse truck, it has a enclosed crate on the back. I have had an unusual noise that starts like a shhhhing noise then turns into a squeal, rather loud.  The noise seems to come from the centre part of the engine.  So far, the brake booster, water pump, alternator, starter motor, clutch, gearbox,and tail shaft have been either checked or replaced and come up with no luck, with in 15- 20mins driving the noise starts. It doesnt matter what road surface, or what speed, it isnt constant, its intermitant, it also never does it when in idle.  It does not affect the running of the truck.  We are out of ideas.  We are replacing the spring on the passenger side as it has slumped, and are going to also put in new shockers, but i doubt that it will have any bearing on the "bagpipe" noise....any ideas.  I was told to check the fan as they are on all the time..but it does not seem to make any difference. The noise does not seem to affect the running of the truck, or the brakes, or steering....I know its a hard one..its a mystery to myself and my mechanic
thanks
katrina

Answer
Hi Katrina, I hate these types of noises. First if this noise will do it at idle, I would remove one belt at a time to locate the source if any. If you removed the alternator belt and it went away then look at what this belt drives. Do this with all belts to locate problem. I hope this helps you. I will be deer hunting the next couple of days so you won't be able to contact me.

Mark