Vibrating Penis

It's probably just a rush of blood flow through a vein at one time or another. This may be quite normal. I don't think it's anything to worry about unless you start to feel pain or see discoloration in the area. If not, don't be concerned. It could be worse if there were no pulse or flow at all.

 

Somewhat related but not related. My friend who has kidney failure just had a fistula implanted in his arm, which will serve as a site for hemodialysis of the blood. Interestingly, when one touches the area just above where the fistula regulates the blood, there is a strong vibration feeling - almost electrical even, like a buzz. As far as fistulae go, it's actually a good sign that it is working. So, I'm not surprised that a vibration could be felt elsewhere in any vein.