I'm new to this site, but believe this will be a good place to seek some information. I've been commuting on an izip dash for approx 6 weeks now. Over time, I noticed a very slight intermittent vibration that I determined to be coming from the rear end. I've never had a bike with disc brakes and figured that was the likely source of the vibration and what feels like some drag in the back wheel. I have since had the rear brake adjusted twice, the last of which the mechanic showed me that the brake was properly adjusted, and completely loosened the brake cable so I could see the disc move between the pads, without rubbing, and the back wheel still made the intermittent vibration, and definitely has drag compared to the front wheel. I suppose I might expect a bit of slowing as the rear wheel spins, but the wheel might make 2 rotations before coming to a complete stop, when forcefully spun. Is there anyone on here that has had a similar experience, either with the sensation of drag, or of the rear wheel hub rubbing. . . .something? Any input is appreciated.