Question

I recently bought Eris E5 studio monitors and a Temblor T8 sub. I connected the two monitors to the sub via a TRS balanced connection and the only port I have to my pc is an auxiliary 3.5mm, so I had to connect the sub to my computer with an RCA to aux cable. The monitors have a horrendous white noise to them that I can't get rid of even by lowering the gain. I have plugged the aux cord into my phone and played music off there just fine without the noise. I'm not sure what other information to add here because I don't know what the problem could be. I can provide any other information if needed.

Answer 1

The problem is the noise floor of your PC Audio is not very low, as a result you are hearing the noise floor of your system in the output of your speakers. 

LifeWire.Com has a good article on what Noise Floor is. 

Our suggestion would be to use an audio interface that has a lower signal to noise ratio such as one of our USB Audio, 1394, or Thunderbolt interfaces that will lower the SNR for your monitors. However even the Studio Monitors will have their own SNR and depending on how high you have the amp cranked, you may hear the noise floor of the monitors when no audio is passing through it. 

Answer 2

i compared 3 different  monitors with same audio interface without any noise, Very Shame !! that noise is built in with th speaker !! poor engineering and lack of the basic monitor construction knowledge , i can't believe a company like a presaonus make such a problematic monitor !! and they still advertising and selling it !!