bad check valve maybe??

So I was letting the compressor run a bit before I left work today, and suddenly it got quiet(still running, then it got really loud, almost like metal resonating, and then it ran fine, and went back and forth with the loud and quiet.  I reached under and held the head of the compressor and didnt really feel any difference in it.  The only thing I could think of is maybe the check valve that is inline between the compressor and tank is bad????  Its one of the square style SMC ones I got from SuicideDoors a few years ago.