[Protonus]

1.) What program are you playing music in?
2.) What program are you playing video in? What kind of video?
3.) Are you using an external amp with the phone? If you're an audiophile I'd expect you would be.
4.) Do you have wi-fi or bluetooth enabled or in use during this testing? Both generate significant RF which could be affecting the circuitry of an unshielded offboard amp.

I have tested MP3 audio in CorePlayer and WMP and found no outside noise. I tested video in the same programs that was converted using the HD video converter on the PC from a 720 x264 source, and again, no external noise. I actually did have Wi-Fi and BT on in my tests too, though I wasn't actively sending data. This is with modified JVC Marshmellow 1st gen canal phones. Before you get high and mighty if you're not familiar with these canal phones and/or canal phones in general, look 'em up. But for the money they are some of if not the best portable listening 'phones around per $. They are very sensitive (as are most canal phones), and being that they are foam isolated canal phones they block a tremendous amount of outside noise resulting in a very isolated listening experience, in short if there was noise, I'd hear it on these I'm sure.

Now the thing with canal phones is due to their effective sensitivity I'm able to listen at much lower volumes then with other devices, so I'm wondering if with your big / fancy full size phones if you're overstressing the amp and clipping or picking up noise because of a higher volume setting and subsequently higher line voltages. Again if you're not using a external amp with nice phones you should be for that reason. I know that the audio output via the 3.5 is a little low and I'm sure that's why HTC included that "booster" app for those that like to go deaf. But even with my canal phones, with that booster app at stock settings, I'm listening at 100% volume in WMP and 50% system volume with plenty of volume...