I had one on my Turbo 36 - I think 'Whisper' is a trade name used by Mastervolt - it was a Farymann diesel with a Paguro alternator, as indeed are most of these small ~ 3.5 - 4.5kW rated gennys. Many many of these are the same thing with a slight variation on the external package - Westerbeke; Mastervolt; Paguro; Fischer Panda, etc.
If you need parts avoid using the make name and apply some common sense searching techniques. I needed a new blister panel for the starter, and Mastervolt wanted > £300, so I bought a Westerbeke for ~ £20. Farymann parts - never ever from a Marine parts supplier - go to Mitcham Diesels (Diesels UK).
Watch out for wear / corrosion of the exhaust valve, as this is a very common problem and when it happens will need a new valve seat fitted by an engine shop.
I have loads of manuals if you end up owning one - so just PM me.
Mine is a Whisper 3.5 from Mastervolt (now Whisper Power - Mastervolt sold the business a good few years ago). It has a Kubota single cylinder OC60 engine, so doesn't sound like the above poster's generator. There are those who claim that running at 3000 rpm must mean that it's unreliable, but I haven't found it so.
Plus side is it's small and the sound proofing quite good, and so far reliable as a generator (engine & alternator). It has, however had a couple of exhaust temp sensor failures, so a spare is a useful thing to carry. The really bad thing is the Mastervolt control panel which is extremely badly conceived for a marine environment (lots of posts on the subject, eg here).