When I had these issues I did not have my Sony MDR-7506's yet and I thought I may have been having these issues due to using mediocre Apple earbuds.
Unfortunately that was not the case, when I received my Sony MDR-7506's on 10/22 I still had issues 1,3 and 4 but issue 2 went away. I decided to take the following troubleshooting steps in this order.
1. Re-seat card
2. Use different molex connector
3. Move card as far away from GPU and PSU as possible
4. Give the soundcard it's own modular lead from the PSU to ensure clean power.
Unfortunately most of these steps did not work except for step 3 which had a SLIGHT reduction in buzzing.
Here is an example of the buzzing and hissing I have been hearing:
WATCH YOUR AUDIO LEVELS
Any suggestions are welcome :)
Thanks,
Ken








