What are you using as the output from the PC, the sound card's output jacks? Using the analog outputs?
There are usually more that one volume level control you must set, such as in the Windows Sound option. Or the one that appears as a speaker icon on the lower right side of the screen. That might help with the high volume level, and possibly the noise.
Frankly in my experience, either a mother board interferes with the audio output, or it doesn't. If it does, there is little to nothing you can do about it. I've had boards that were dead quiet like you mentioned, or ones that even allowed the movement of the mouse to be heard as noise, again as you mentioned.
Other suggestions would be disabling all the other audio devices on the board, in Device Manager. Is your sound card selected as the default audio device in Windows? Try moving the card to a different PCIe slot, and keep all cables of any kind as far away from it as possible. Are you using a wireless mouse or keyboard? The RFI those produce could be adding to you noise problem.
If you mute the output of the audio, can you still hear noise? If so, that is a dead giveaway that the noise is being added after the audio signal is processed by the card.
On some boards, I had to use the S/PDIF output to an external DAC, etc, to be able to use the audio, since I could not fix the noise issue. I'm so conditioned to expect bad audio from a PC, I don't even check it anymore.