Having a buffer or spring rattle is very normal. If you are talking about the buffer itself making noise, that would be the weights integrated in the buffer rattling around slightly. Which is once again, normal.
As long as your buffer tube uses a carbine length buffer, it will accommodate this buffer weight.
You would likely want to stick to the model meant specifically for .308:
https://www.opticsplanet.com/primary-weapons-systems-pws-enhanced-308-short-recoil-buffer-mod-2.html
No, it is just the buffer weight.
Yes, this will work with a mil-spec buffer tube and also any other buffer tube that accepts a carbine length buffer.
Higher numbers (H2, H3, etc) mean a heavier buffer. In theory, heavier buffer = less recoil.
Yes it will work with any carbine buffer tube.