If you do suspect the keg the first area to look for problems would be the top valve in the keg well. There is a raised coated ring on the inner diameter of the valve surrounding the steel ball. Take a paper towel and wipe out any liquid on top of this area. Using a flashlight, inspect this ring for any tear, cut, crack or gouge. If so, the pressure will be routed directly into the beer stream as it leaves the keg.
Scott Zuhse, Instructor
Micro Matic Dispense Institute