I own and shoot crossbows, so I will try and help a bit.
There is a minimal amount of noise in cocking a crossbow, but often an audible *click* to one that has some sort of locking mechanism. Think of those road devices that police use, where you can drive over one direction, but not the other. The string passes it easily enough, then *click* it is held until discharged.
My father's crossbow is 90 pounds (He has had it since he was a kid...50+ years,pretty awesome. My strongest crossbow is 150 pounds draw weight, so it would be at the top end of 'light', especially if one looks at some of the crossbows from 500 years ago etc...
Some Gamer will undoubtedly come forth with WIki'd info (I do it, we all do it) about some 400 pound draw from this or that crossbow, but for a standard portable one, 150 is pretty strong. My brother and I used to shoot it through truck tailgates in an old lot.
Anyways, with any sort of windlass device, there will be noise, likewise, with a cocking lever. A foot stirrup/goat's foot/paw won't add noticeable noise (Other than from the user, I have been known to 'Oompf!' a bit when sore, after shooting all day).
As far as carrying it, it is possible, but unless there is some sort of safety device, dangerous for anyone in front of you, and definitely dangerous if you are moving over difficult ground/quickly. As much danger for the crossbow (Which will take damage if suddenly thrown to the ground) as to the user from accidental misfires...
Hope that helps a bit.
-Uriel