I have a 2003 with the 4.3 engines. I was just coming on here to ask the exact same question. After 20 minutes of the boat running I get the 2 beeps/min alarm. Nothing shows on the mechanics computer. He thought it might be the block pressure sensor and it was not. I can not figure this one out. Gauges reading perfect, gear oil is good.
Figure anything out yet? I'm in the process of rebuilding my seawater pumps to get my beeping to stop.