As for the hiss coming from the fueltank cap... When it's warm out, mine always does that.
When my one riding buddy said something about it once, I told him that's the hidden power of the Vulcan waiting to be released, then, once we were on the road, I blew his footpegs off as I passed him !! LOL
When we stopped for a smoke break, I reminded him of the "hidded power hiss", and he just mumbled something about "well, if we had another couple miles, I would've caught up to ya"
I just laughed and said "Yeah, I would've slowed down to wait for ya"!
What I'm saying is, I believe the tank hiss is normal.
AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC
"When life throws you curves,
Aim for the apex."