Transmission grinding and wont go into reverse

Is the knocking sound when the car is moving or sitting still as well? Does the grinding sound happen just as you put the car into reverse or does it keep grinding?
These transmissions are very problematic, especially if they are not properly maintained. The most likely candidates are a cracked flywheel or a broken drum inside the transmission. Either way, it sounds like the transmission will have to be removed to pinpoint the problem.

replace transmission common problem

you need a new reverse gear. the rest of your transmission should be fine but it will need to be rebuilt because you probably have pieces of the reverse gear floating around in it. it will eventually ruin the transmission if you don't fix it soon.

Reverse is not "synchronized" forward gears are, so it does make some noise, try shifting to 2nd before engaging reverse to slow gear rotation and limit gear clash or grind.

sounds like it is time to get the transmission rebuilt. usually when they go out you will only have reverse. It sounds like the oil pump has exploded inside the trans. sorry for the bad news

is it grinding when you try? try to turn car off hold in clutch put into reverse and then start car
if it pops right out you need to get it to a transmission shop.
i recently replaced a transmission in an SXT that had no reverse, all it would do it grind and pop back out

Yes it is and more it internal transmission failure

Check up and adjust the transmission cable, shift rod, and selector fork of gearbox. See picture below.

Your transmission obviously has a problem. Take it to a transmission repairer.

Problem is likely either a worn shift fork or bad synchro (both inside the transmission) It's unlikely that you have a clutch problem otherwise the problem would be with first and reverse and shifting other gears would also be difficult.