Unit is three years old. Within the last couple weeks I replaced all four duck bill valves, the vacuum pressure switch and the heads seals etc... But as it did before I did all of that, it still pumps/cycles about every 20-30 minutes for about 20 seconds at a time. I cannot locate any leaks and am at a loss for what to do next. Thought about maybe adjusting the pressure switch, but have heard some people advise against changing it from the factory setting. Any thought?