The sounds you are hearing are probably coming from the internal workings of your PC, but I did find the HE-400 a bit tinny sounding and they distorted with my system on some tracks. Perhaps that is what you are hearing. You may want to look into an external DAC that will virtually eliminate the noise coming from inside your Mac.
The HE-400 and to some extent the much better HE-500 sound pretty unexciting on some tracks / systems. The HE-500 is much better sounding it that is has virtually no distortion and not tinny sounding at all.
Personally I never recommend the HE-400 as I find it far inferior to the HE-500 which I consider the budget Ortho.
You may want to keep an eye out for a Denon AH-D2000 or AKG K550 and give those a try. I think you will like the sound signature a tad better if not much better.