Can I use REW to diagnose system noise electrically?

First, a little long-winded background…. So, I’m busily working my way through understanding REW at the same time I’m fighting a few problems in my system. One of those is chasing down sources of ground loop humms and noise using the the Jensen Transformer troubleshooting kit. Then, while running around and reading FAQs and older threads, I ran across this post: :

http://www.hometheatershack.com/forums/rew-forum/9872-spectrum-rta-feature.html#post86006

(didn't want to include it, as it's quite lengthy, but just look at the first picture. If someone can tell me how to include it directly - all I get is the Attachment # - I'll edit this to paste it in - thanks!)

It left me wondering: can use REW to directly measure the electrical noise going INTO the speakers. I know I can hear hiss and/or humm on the speaker, but measuring it electrically would seem to remove differences in mic setup or ambient sound levels in the room and make it easier to quantitatively measure what effect different fixes bring. I didn't find this procedure already described, but I may not have looked under the right search terms. Is there something I missed?

I figure that I need a simple circuit to convert speaker-level voltages back to line-level (or just to read them off). Would probably like to have it with an RCA line-out so I can just plug it into my sound card line-in and complete a loop just like we do in calibration. It seems like it would be an easy circuit to build. Or is it something that’s already available - I didn't find anything on search terms I could come up with?

Hope I'm not :coocoo:.

I hope I'm :coocoo: like a fox!

Thanks