Hi,
The noise you described is caused by the clutch shaft splines that run the PTO, turning against the PTO clutch splines, when the PTO is not turning.
The splines in both parts could be worn, or other things can cause it. If you read everything in the post Jim B. posted above, that has info about what to look for.
The Cub owner's manual can help you learn about maintenance that the Cub needs.
The service manual in the link in the post above is more for use when the Cub needs repair.
Below is the 1949 Cub owner's manual. The experts on here recommend people read it. It has lots of info about operation, maintenance, and lubrication. There is a table of contents on page 1.
It shows how Cubs originally looked in it. The lube section begins on page 14.
http://farmallcub.com/rudi_cub/www.clea ... index.html
It shows the electrical system that a 1949 Cub originally had.
Cubs made before mid 1964 originally had 6 volt, positive ground electrical systems.
The 10 weight motor oil mentioned in the manual for the Touch Control was changed later to Case IH Hy-Tran fluid. It is sold at Case IH dealers.
There are other brands, be sure it works with IH hydraulic systems before buying one.
The manual tells how to check and change the Touch Control fluid, and remove the air from the system.
Be sure to check the fluid with the arms in the rear, or down position, the manual says to also.
I would check or change all the oils before using the Cub. Using it with low oil in a gear housing can damage the parts in the housing.
There are 3 separate gear housings, with 3 separate oil levels to check, in the rear area of a Cub, the transmission, and 2 final drives.
The transmissions in Cubs commonly get water in them, from rain, or condensation inside the housing over time.
The air cleaner is an oil bath air cleaner. Dirt that is sucked in settles to the bottom of the oil cup. It should have clean, light motor oil in the oil cup to work right.
There is a search box at the top of the page, to the right of the Farmall Cub, you can find info in posts that have been made.
Below is the Cub 22 Mower owner's manual. It has lots of info about the mower.
You don't use the manual lift lever shown in the manual if the Cub has Touch Control.
There are manuals for other Cub implements at the top of the page at Cub Info, then go to Rudi's Manuals, then Cub Implement Manuals.
http://www.farmallcub.info/galleries/ci ... _Mower.asp