I know Uriel....I'm not so sure there isn't a glitch with the vampire attack Towns feature, the second character I started to run thru dg hasn't had as many attacks. I'm still getting a fair amount, but at least it's not constant attacks like my other one
I'd say that the first game has a glitch in the randomization algorithm. All of my games are like your second one; I have attacks, but they're not constant. They happen more when I Fast Travel than when I run around and arrive at a city via Shadowmere/Arvak. Your second game, the attacks are happening as they should.
But like the Dragon attacks, they'll increase in frequency as you progress through the quest line, but once you complete a questline they'll drop off considerably.
Don't lose heart, I'm sure they'll get the randomization math correct in the next patch, or at least be able to ferret out what exactly the glitch is and isolate and fix it at that time.