The ticking sound is normal, at least for my coach. Remember, for diesel engines to start, their "glo plugs" or "piston sleeves" must be heated first, and this takes several seconds before they roar to life. Diesel engines have a totally different ignition system compared to gas engines.
That's why when you turn on your ignition key, at least on my rig, I have to wait to start the engine until a light on the dash goes off. Then, the piston sleeves are heated and ready to go. Same thing for your generator.