[jonathan150cc]

Does anyone have any experience with manual treadmills?

I've been brainstorming about how I can keep my legs moving and generally be more active while I'm at work. I thought the idea of a huge electric treadmill would be a little cumbersome and noisy and I thought to myself that someone should invent a non-electric treadmill.

Much to my surprise, I discovered, via the wonder that is Google and Wikipedia, that manual treadmills have been in existence for quite some time.

After I stopped crying from the pain of realizing that I hadn't come up with an ingeniuous invention, I started searching and found several for about $30, used.

So, back to the question: Have any personal experience?
How noisy are they? How does that noise compare to the electric kind. I don't want to be disturbing everyone around me. They don't mind my moving around, but they probably wouldn't much care for moving around and hearing a constant "whir, whir, whir, whir" sound.