[eggsuckindog]

I don't think they have one -

if you disconnected the water separator it must be in the oil circuit, although I drain the separtor every now and then to check whats in it. Although since its only 1 beep apparently, it may be a glitch in the module itself, have you made sure the motor oil tank is dead full? Mine was giving a quick beep every now and then too, I went to the water separator since I had some in it a month ago- nope the oil tank was just a pinch low I guess?
On mine I'm thinking maybe take the main tank cap off to make sure its sealing correctly, as it would take a couple minutes to re-pressurize if its leaking down. Didn't appear low when I looked but must have been just enough to bounce, bled it an no issues.