Going to be louder than a home unit because it is sitting in there with you.. but.. most of the time loud noise (relatively) from a unit like that is caused by a moving part hitting a stationary part.. so you can start by looking for places where the compressor or its piping might be hitting part of the boat structure or furniture.. Another place to inspect carefully would be the compressor shock absorbing mounts.. these are normally kinda soft rubber and can be pushed out of place or improperly installed. Another place to look is the pan of the unit. The pan is the base plate and if it is not supported underneath, it can make some loud noise. Sometimes the best investigative technique is to grab and push firmly on parts until you find the place that stops the noise. Use gloves because the compressor and its discharge tubing can be very hot.. Happy hunting ..
Many units like that were installed by dealers or owners and not by the manufacturer.. Usually, if you have a model number and brand, you can find a manual on the internet..
