I have been severly dissapointed in the GL1800 intercom system since day one of ownership.
The intercom system has three basic problems wrong with it. They are:
1. The intercom amplifier itself has in internal design flaw that causes the audio unit and top shelter to act like a microphone. It picks up and amplifies road, tire, engine, and wind noises, and sends them to the headset. The higher you turn up the volume on the intercom, the worse it gets. Try tapping on the top shelter with the intercom volume set anywhere above 10, and you will see what I mean. It is just a real poor design of the amplifier circuits for the mics that is causing this. Honda should have fixed this 3 years ago. I think they are just now figuring out they have a problem. I highly suggest you call Honda Customer Service and complain, and take the bike to the dealer and complain.
2. There are no filters in the intercom amp at all to filter out wind and road noise frequencies. This means that at any speed above about 60-65 mph, intercom operation becomes very dicey at best. You are almost better off turning off the intercom and yelling at each other above about 65mph.
3. The 2001 and 2002 bikes had a lot of alternator whine in the Headset. Honda fixed it in the 2003 models with a new headset harness and inductor on the ground of the audio unit. You can order the harness and retrofit a 2001 or 2002 model, but you have to buy the harness yourself. This new harness only address the alternator noise in the headsets and does nothing to help problems 1 and 2 stated above.
I resolved my intercom problems by installing a complete Autocom system on the bike (about $500 including headsets). It works 400% better than the stock GL1800 intercom.