If the main clutch is failing, then it would be difficult to change gears without "grinding gear noises".
You should also know that in a MF tractor with Multi Power, that it can be difficult to change gears when in High Multi Power. Switch to low Multi Power and try again. Seems like there are at least four items that one should know before using Multi Power:
1) free wheels downhill when in low Multi Power.
2) hill hold feature when in high Multi Power.
3) difficult to change gears when in high Multi Power
4) can not pull-start a tractor with Multi Power.
Many of us had hundreds of hours on a MF tractor with Multi Power before we bothered to read the manual. I know I did.