Reply to Hissing Noise From Speaker Help

I bought this 50$ heavy duty power strip called Furman SS-6B Pro Plugs and i tested out my new 100 watt speakers that i hooked up to the p.a mixer to my audio 2 to my laptop and I noticed there was a hissing sound that would come and go. After missing with it Alot i noticed that it was the usb port i was using on my laptop for some reason. So i figured that out but Im still hearing hissing every now and then wither im playing through my speakers or monitors.
I have heard of dirty electricity and am now assuming it has something to do with that since i cant figure it out.
But the power outlet that was sold to me was post to eliminate that i thought.

"On the box it says EMI/RFI Filtering reduces Distortion and Hum from AC Line."

I was looking to buy a power conditioner for this reason but was redirected to buy the furman ss-6b cause my speakers don't need a power amplifier apparently.

If you or anyone you know has an answer to this problem i would be very grateful.
Thank You