Yah I have heard of and seen videos of guys with weights on their bow strings. they just look like the brass nochs but there are a few of them. about 4 or 5. I only know they are weights because that is what the people in the video refer to them as.
They're generally referred to as speed nocks, and the engineers at the manufacturer tinker with them to find the best return on their placement as well as amount to reduce string oscillations and improve arrow speed.
