[Franke]

I agree with Schrade that the diaphram is rupturing. So with that said have you checked the fuel pressure coming into the regulator? With the ignition on and engine off the pressure should be 48 - 55 psi. If higher than that then are you getting any codes or exhaust odors?
According to the manual the return line goes directly back to the tank. If you have a restricted return line, fuel pressure will increase . Like Schrade says, check for a restricted return line somewhere especially any rubber fuel line connections.