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Try pushing the compressor from side to side with your hand to make sure that one of the pipes outside the compressor is not rattling.
If it still makes that noise the odds are in the 99.9% range that the crank shaft rods are worn, and loose and may not last a lot longer. There is nothing else that I have ever seen that will make such noises.
Here is a story for you. One time about 40 years ago I was called to work on a large fish storage freezer... it was running OK but just not quite as cold as the customer wanted.
I removed the valve plate. All three pistons had stopped at the top....(that is not possible unless two rods were broken)... I turned the compressor on with the head and valve plate removed, and only one of the pistons went up and down, it had been running for a year or so apparently on only one cylinder and still keeping the fish frozen.
If you want to test for loose rods, remove the valve plate and use a rubber mallet to hit each piston on the top when the compressor is turned off... if you hear a loud click then the rod on that cylinder is loose... try it many times, you will only be able to detect the bad rod when the piston is either near the bottom or top of its stroke.
We can go from there.