These Currie brush motors have always made the same buzzing sound, but it's not irritating. There have been many versions over the years, the original one was a lunatic, incredibly fast and powerful but overheated and burnt out. When revised, it lost a bit of the power and gained a huge finned heatsink, but with time was able to lose that and also become more refined, ending up with the present series. I don't think the motors are convertible to different powers now, and there's several drive transfer systems in existence. There's the fixed to the wheel transfer arrangement as on the IZIP, a kit version with a clamp on boss for 36 spoke 3 cross wheels on any normal derailleur or fixed gear bike, and I've heard of a toothed belt drive version but never seen it. Most seem to have disappeared these days as the Chinese increasingly take over everything bike with their own designs. There used to be various "go faster" items available in the USA, such as different motor internal gear sets for other speeds, mainly faster, but I can't find trace of them currently, though I'm sure they must still be around.
