Never rode one, but I thought about buying one until I priced them. I was at Eureka last weekend, and there were several out on the trails, and I did not notice they were any louder than any other atv/utv out there.
Just got one a week ago. Have a little over 100 miles on it and am very pleased. Very stable due to how wide it is which is great other than when you hit a tight trail. Rides very good. It was a bit loud so I added a Silent Rider exhaust silencer behind the stock muffler. Have also been reading about a few custom mods to quiet the inside down a little. I did a ton of research before pulling the trigger and it seems as though Yamaha did their homework when building the Viking. Check out a few YouTube videos comparing them to the Ranger and Pioneer and see what you think. I really have no complaints after the first 100 miles. Many things I like about it better than the competition.