Sometimes when I start up the pressure will build to 30 psi and stay there for quite a while then go to 120. Once it gets to 120 I occasionally hear something popping off under the hood. Nothings open or leaking. I think this truck sat for a year or so before I got it from GL. I did a search and found a reference to taking the regulator apart and cleaning/oiling. Has anyone done this? I also read where some have reduced the pressure to 100psi with an adjustment on the regulator. Should I leave it at 120 or reduce it? I'm the kind to not keep anything at the max if it's not necessary.