Good observations and recommendations above. I would just add the following:
1. Noise is not likely related to the 802. Any radio would likely be hearing the same noise (RFI).
2. RFI can be extremely difficult to find and eliminate, even for very experienced radio folks. You have to work
at it methodically. The steps outlined above are good ones.
3. In addition to those mentioned above, there are several things to check:
a) the power line to the radio. Power should be taken DIRECTLY from the house batteries
, with appropriate fusing near the batteries
on both the positive and negative cables
. It should be a minimum of AWG6 cable for one-way runs up to about 20', and AWG4 or even AWG2 for longer runs.
Note: this is important not only to get full voltage to the radio, but to help eliminate RFI both ways...from the radio to other instruments on board, and from other equipment
on board to the radio. Going thru a DC panel is NOT a good idea.
b) use of RG-214 coax between the radio and the tuner....this is double-shielded coax which is the same size as RG-213....also helps reduce RFI.
c) the RF ground system should NOT be tied to any other ground system on the boat (DC, bonding, or lightning). It should be entirely independent.
d) inasfar as possible, run ground system and antenna system wires away from other electrical
wires on the boat.
These steps are IN ADDITION to others mentioned above, but can be implemented in any convenient order.