Do power conditioners help with unwanted hum/noise

Sometimes they can help. The most graphic illustration I can think of is that I used to have a pair of Martin Logan Prodigy speakers. They had a little blue "ML" logo that lit up on the front when a signal was present; if a signal was not present for a sufficient time, they would actually go into sort of a shutdown mode. But, the little blue lights were always on in my house. Until I got a power conditioner. As soon as I did that, the little blue lights went off. So, there was obvious some kind of line noise impacting the signal path.

Oh yeah, it sounded better too. ;)

There are some other solutions for cable connections--like the "magic box" or somesuch. If you think the hum might be system related (i.e., post power conditioner), could you try unplugging other components to see if it goes away?