That "slight whine" sound is not encouraging. It sounds to me like your Hydro pump may have had a failure. Based upon your description, it sounds like the reverse will not work when the weight (load) of the tractor is upon it but you were able to get the rear wheels to engage and spin backwards when you had the tractor jacked up and blocked, correct?
How long has it been (hours) since you serviced the Hydro fluid? How many hours are on the tractor If I recall, it seems like your tractor holds 17 quarts of Hydro Fluid in the Sunstrand Hydro system.
I will tell you that I had a JD Hydro on a 22 hp Yanmar that became very sluggish. At the same time, I noticed the tractors power steering began to "feel heavy" and then the steering would only work intermittently. I flushed out the Hydro system and installed a new filter and it is still operating 500 hours later. When I say I flushed out the system, I completely drained it, filtered the old fluid thru a fine metal colander screen and coffee filter combination and carefully checked it for metallic debris. I then filled the system, ran it one hour and drained the entire system once again and screened it and installed a new filter. Yes it cost a few $$$ for Hydro fluid and filters, but it continues to function just like when it was new to this point.
I opened my hydro filter and it was "collapsed" internally causing a major fluid impediment. I have the right tools to open the filter correctly so the opening doesn't create metal shavings, fragments, etc., as I always inspected my race car motor oil filters on every fluid change.
No fluid leaks anywhere, correct? Do other hydraulics work correctly like FEL, rear PTO, etc? I would check Service Manual for info about relief valves on that tractor as well. Especially if all other hydraulics are working correctly. Wonder if the whine you are hearing could be a relief valve stuck open......If it is more of a "grinding whine", then the valve is likely out.
I see the Service manuals are about $25 to $45 from various sources. Definitely want one of these to help with any diagnostics. Please let us know what you find.
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