So This afternoon, I went to start my car and there was a awful rattling sound coming from under the hood, after locating the rattle, it seems to be from the bolt that adjust's the tensioner. My question is, is it the pulley or the whole system that needs to be replaced???

 

Why not just tighten the screw or if it was never replaced, just replace the pulley which will come with a new bearing.

 

is it the Adjuster bolt? or the bolt holding the tensioner pulley itself?

 

The tensioner nut that that points to the sky rattles on mine sometimes too. I just preload it with a ratchet to take up the slack.