Speedaire 3Z180 makes popping sound
I have a Speedaire 3Z180 pump with 5 hp motor and tank. At 100 psi it starts to develop an occasional popping sound and as pressure builds, the frequency increases to about one pop every other cycle of the flywheel. The pump will develop only about 150 psi. I have replaced the valves and there was no improvement. I cannot tell exactly where the sound is originating from. Any ideas on why the sound and how to make it develop at least 175 psi?