The best way to determine the noise level of a generator is to have the retailer do a demonstration run of the generator for you, so you can actually hear how loud it is when it runs. RV shows are great places to hear and compare different kinds of generators. Some manufacturers give generators decibel ratings. A quiet generator has a 50 to 60 decibel rating, which is about as loud as a normal conversation.
Sometimes generator manufacturers try to influence customers' purchasing decisions by giving the decibel level for the generator running a low load, rather than a full load. This is why hearing the generators in person is the best way to find a quiet generator. The noise level may depend on what appliances the generator is running. If the planned use is low and you intend to run the generator at limited capacity, getting a generator that is loud when it runs at full capacity may be okay.
Newer generators are generally quieter because of technology advances. Besides RV shows and camper showrooms, customers can ask fellow campers who have quiet generators which brand they have in order to discern which generators run quietly with normal use.