I was reading over your post and thought that the below listed articles I found will be of some help to you in understanding how the Slingbox works and why you may be experiencing issues with no video and hissing audio.
However, be sure to check the connection of your cables. Ensure you are using the correct cable to the RCA jacks throughout the cabling. I.e. component to component, composite to composite. You can also test the cables to ensure that they are not bad by connecting them directly from the cable box to the television set to see if you get clear video and audio on the right source input for your television (component/composite).
I hope that the above information and article links are helpful.
I have good audio and video on my PC on my home network, thereforeI don't think I have a connection problem at the slingbox. Does the video leave my home network to the internet, If I log into Slingbox.com to watch TV? Does this just enable my PC on my home network to accept and process the stream from the slingbox internal to my own network? I would like to narrow down which end to troubleshoot.
I set up my Pro HD and can access my PVR that it is connected to from my Windows 8 PC at home. I do this by going to: www.slingbox.com, log in, watch. This works OK. I assume this means I am accessing the stream via the internet since I log into my account on the web. So the stream goes out of my network, then back in. Am I correct? I tried to access the stream remotely from another PC and Android devices, and I can log in to my account, see the Pro HD, access the guide, but all I get is a black viewing screen and hissing on the audio. What is the next step?