bilge noise forward head


Greetings all.
I have a 1998 Amel Supermaramu #230. Guests who have stayed with me
have noticed a very annoying noise problem in the forward head area.
I wonder if anyone has dealt with this:
When the generator is running, there is a noise that can be heard in
the bilge piping at the forward head. The noise is intermittent, and
sounds like air pockets intermittently developing in the bilg piping.
In trouble shooting this noise, I have been able to stop the noise
by: 1. turning off the generator, or 2. leaving the generator run
but opening up the engine compartment ever so slightly. This all
seems very mistifying to me. Any ideas?
S/V Bel Ami

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