Rattling/knocking noise

I used the belt map to locate where it appears to be coming from. The man who owned it before me kept up with the maintenance really well so this is the first time I have seen an issue since I bought it.

The noise "sounds" like it is coming from the idle pulley under the A/C compressor. To be sure, I unplugged the A/C compressor and took a closer look and it looks like the idle pulley is shaking a bit more than everything else next to it (they appear to be stationary).

Any clue if this is accurate?

The image is the belt map. I unplugged two from the power box and when physically looking st it, I "think" the noise is coming from six.