I want to add my experience with the USB-interface. I have been using a USB-soundcard (Soundblaster X-Fi Surround 5.1 Pro) since the mid-00's, I have used two headphones on it: an HD598 (which was rebranded as the HD599) and an HD700, both from Sennheiser.. A recurring problem which I always had was arbitrary crackling noise. I can only describe it as similar to what you might hear with an old LP but much stronger, or similar to when you burn wood in fire and hear a crackling sound. Here the interesting thing: it doesn't matter which USB-port you use, it can come any time on any port and sometimes switching the port helps, sometimes it doesn't, sometimes leaving it on the same port and booting the computer again solves the problem. i have had this on two different systems, an Acer prebuild and a computer which I assembled myself (3700X, X570 Gigabyte Elite). I have used multiple operating systems: Windows7, Windows10 and several Linux distros. Some operating systems (W7) have this worse than others (Linux distros) but on all operating systems you hear it in some way. On Linux distros it seems to be limited to when you change the volume by moving the slider with the mouse (not when you use a keyboard-button to change the volume), on Windows7 I had it all the time when just watching a video and it could get loud. I agree with the topicstarter that we should look at the measured data but I also believe that maybe not everything which is relevant gets measured. Maybe the USB-interface becomes a problem when the same USB-hub (which several ports are connected to) is being used for other data too (keyboard, mouse...). Maybe the USB-interface becomes a problem when there is too much electromagnetic interference from the components on the PCB (like a motherboard). I don't have the answers, I can only share my experience that I had a lot of problems with crackling noise which was related to the USB-interface given that it often disappeared or changed by simply plugging it into another USB-port.