I recently bought a CK20 Manual Transmission with under 300hrs. Yesterday I was attempting to pull a heavy load in gravel. I had 4wd engaged and as the wheels spun in the gravel the tractor produced a clicking sound. It wasn't a grind but I guess could almost sound like that. All 4 wheels were engaged and things were functioning properly. Is this typical or is something going on? I do find that sometimes 4wd is difficult to engage and I have to move the tractor to get the lever to engage. Any thoughts on either issue would be great.