I also have a setup with the m4 and have the same issues. It's a faint noise so not a real big problem as long as music is playing, but still it's annoying and not right. I also notice the noise changes frequency (no audio playing) when I scroll or there is disk access. Engine running or not doesn't make much of a difference. I have a Kingston SSD drive but I don't think that's the culprit. I like the features and how the m4 works so I'm not against them but I would have thought it would have better noise suppression. Unless someone else comes up with a good cost effective solution I'll continue to tinker around with it and if I find something that works I'll pass it along.