high compression on one cylinder?

[Foxfan88]

ok i'm in the process of taking my engine out for new freeze plugs and i was running a compression test as i was tearing her down to see how it was, since the engine got warm since all my water leaked out i was just making sure of any problems i may have.

all cylinders had great compression
all of them were 180 psi except for number 3 cyl. which was making around 210 psi. when i was cranking on that hole i noticed it made a strange sort of popping sound everyime it was on its compression stroke ( sort of like the sound when you hit then end of a tube with the palm of your hand)

other than that things are great, what would cause one cyl to read higher and is it a problem?

 

[Bullitt95]

You could have an exhaust valve lifter that's partially collapsed and not allowing the valve to open fully for combustion gases to escape from the cylinder, causing higher than normal compression. The "popping" that you're hearing could be spent gases coming back through the intake valve into the manifold. Left unchecked, you could end up with a damaged piston from detonation.