I have a 7.5 HP Northern brand 29 CFM compressor about 6 yrs old. For the past few months, the interstage safety valve pops off a couple times whenever the unit shuts off. I changed out the discharge/check valve and it still pops. To me, this would indicate the 2nd stage reeds are not seating off and the full discharge pressure (175 PSI) is bleeding back into the 1st stage (PSV set at 80 PSI). There is no other problem of note. I've priced a rebuild kit and it's over $600! A whole new pump assembly is $750. I'm planning on just leaving it as-is until it no longer keeps up. Any thoughts or ideas?