Whining noise?

[Rodclop]

This is my first post so I will try and do my best on describing my problem.
I bought a 79 Chevy c10 bonanza lwb on the april 15.
Tonight while I driving the truck I noticed a loud whining plus a vibration in the floor board that I haven't noticed before when I opened the sliding back glass I could hear the noise even louder. It happens when acceleration I haven't had choice to check the fluid in rear end to see if it's low could the noise be the rear end going out the truck runs and shift fine.
Plus is there anyway to tell if the odometer has rolled over ever. It showed 12,121 when I bought it

[BADAZ chevy guy]

Welcome to the forum.
It could very well be the rear end.
With the trany in neutral, and the truck on the ground, try to turn the drive shaft and see how much play you have. Should be almost none. Check your u-joints for slop. They usually don't whine as much as they just clunk when shifting into gear from park.
I'd put up on stands and run it in gear so you can hear it. (Just DON'T get under it) Ask me why!!!
If the whine in the diff pull the inspection cover and check it out.
After thought. Listen to the axle bearings while it's up in the air. (Outer end of the axle tube) It could also be a bearing going out.

[Rodclop]

Thank you for the reply the truck did sit for year or so lady owned it she did go start it from time to time. When I bought it I drove it 30 miles home and next day I went and changed oil,spark plugs, wires, brakes and ran fuel treatment thru it. The oil was solid black and 2 quarts low so I was planning on driving couple hundred miles and changing again. Seems to run and drive good for a 79 besides the whining noise now

[bake74]

Welcome to the forum.
It could very well be the rear end.
With the trany in neutral, and the truck on the ground, try to turn the drive shaft and see how much play you have. Should be almost none. Check your u-joints for slop. They usually don't whine as much as they just clunk when shifting into gear from park.
I'd put up on stands and run it in gear so you can hear it. (Just DON'T get under it) Ask me why!!!
If the whine in the diff pull the inspection cover and check it out.
After thought. Listen to the axle bearings while it's up in the air. (Outer end of the axle tube) It could also be a bearing going out.

     Also welcome, I would do this first as described, then I would open the rear and inspect anyway and change fluid so at least you know it has been changed and can see for yourself if everything is ok.