We are back home because we have an intermittent problem and decided
to come back to deal with it rather than wait and be stuck somewhere.

What is the problem?

Bob has his idea, but I'd like any alternate opinions.

We were motor sailing along, as the breeze basically died (although it
was from the predicted direction), and I was in the aft cabin when
suddenly it sounded to me as if the engine was running away. I went
up into the cockpit and said to Bob "What is that noise", and he said
there was someone coming up behind us. (We can't see directly behind
us due to stuff on the aft deck.) But I looked and there was no one
there. Bob slacked off the throttle and then cautiously came back to
speed and the noise was gone.

This happened about twice more. The gauges never moved during this
time - RPMs were the same, oil pressure normal, engine temperature
normal (and Bob checked that with the infrared gauge), engine charging
as normal. Bob checked the bilges and looked in the engine
compartment and saw nothing amiss. The engine continued to run as
normal between times.

We got to Crisfield just after 7 and tied up and went to dinner at the
Cove (wonderful dinner) and then we had a thunderstorm.

So yesterday, we were planning to go down to Cape Charles and decided
that was too far under the circumstances and were going to divert to
Deltaville. This happened once more, so we came home instead.

So what do you think this is?