Klipsch Promedia Ultra 5.1 - Humm problem

Lately I start to hear a hum noise coming from all the speakers and specially the sub because i'm very sensitive to low frequency.

When I power OFF the speaker for more than 30 minutes and then power ON the Hum (like electric noise) is pretty loud
and after about 5 minutes it is less loud but I can still hear a hum coming from the subwoofer but I can also hear it
from all the speakers.

I bought a freeze can and I start the sub for 30 minutes to let it heat up and I then start to spray the freeze nozzle
on capacitor, resistor to see if a particular parts when freezed will make the noise coming louder.

But nothing change.

i'm not an expert in electronic but someone gave me this simple trick of freezing parts to troubleshoot but in my case
it didn't help.

What could it be ?

The speakers are all working but at my ears I need to put the volume level higher to get the same sound level as before.
But I also built a new PC so maybe the souncard output voltage is lower than my previous soundcard.

Any help would be appreciated because I really love these PC speakers and I want to fix them if I can.

Thanks

I tried the sub in another place in the house without speaker and I still get the hum noise.
I would say more an electrical noise not the same hum noise as when you don't plug the RCA cables completly on a stereo system.

I have nothing plug in the sub, only the control box.