It's making noise because it's on the way out, low on freon or the belt needs to be adjusted. A loose belt will result in not enough pressure build-up for proper operation and could mislead you. They kind of sound like they have a bunch of large nuts and bolts rattleing around inside. Especially at idle.
So I would snug up the belt first. If the problem persists, have the system checked for leaks when adding freon. Then go for the compressor. Sounds like you may have a hose leak. If so now is the time to replace them all. If there is any good news here it is that your compressor with a new clutch is probably the least expensive of all to purchase. If it's bad - buy new as already mentioned.
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