Upnatm,
That's a good place to start. I have worked in electronics all my life, even while as a kid (no one paid me then - I just did it because it was COOL!)
But, I learned one thing very valuable. The theory of DIVIDE and CONQUER. I tell you this because it is your post and you asked the question, but I am hoping that others will read it, too.
When do you hear the BUZZ? Only on S2 channels? Or all channels? Is it only one S2 channel? Ask others if they hear audio trouble on that channel. No one but you has this audio trouble? Must be your system. What part of your system could cause such a problem? Enter DIVIDE and CONQUER. What is it? It means to break down your entire system into simple, isolated blocks and perform a troubleshooting process on each block. Start with the least expensive and simplest component and either check it or swap it out with a known good component. Audio / video cables? Easy and cheap! Check them first. TV? You probably have a TV in another room, try swapping the TV. TV and cable swapped? Problem still present? Try a different audio output on your IRD if one is available. Problem went away? Problem is with that audio output circuit inside the IRD. Send it in for repair or use the alternate audio out. Well, it may not work out this way for you, but do you understand the process of elimination that I tried to run through? You break the system down into individual components and evaluate the results. This enables you to isolate the source of the problem. Then you may start to troubleshoot that piece or component. If it is a hardware fault within your IRD, you may not be able to repair it. But, at least you know where the problem arises from and can explain it to someone who can repair it with really good background information. They need your information to speed up the repair process, if possible.
Do your best to troubleshoot your own equipment yourself, it might save you a lot of money in the long run. If it turns out to be simply a bad cable, heck, that would be a very inexpensive repair. If the problem is more intense, then at least you have the info to work with and discuss the problem with a technician or someone here with some background in electronics or with your particular device.
The main thing is to PROVE that it is this or that device that is creating the problem.
Hope you find the culprit and 'git er' fixed!
RADAR