Hector Martin

USB buzz is worse; anywhere with a USB and audio ground loop ends up with some horrible 1kHz whine that varies depending on USB traffic. And suddenly you can hear the activity of your USB flash drive again. This stuff is everywhere, even professional TV production. USB2 sucks.

i had a 12V car usb charger for my iphone and when i also connected its headphone port to the car's aux input it would make a horrid noise proportional to the instantaneous power draw; everything from LTE modem to touching the screen to iOS animations made different horrid sounds

I get the same except it tracks the engine RPM, which I can only assume is some weird harmonic noise from the alternator.

i had that as well, i don't remember if it turned out to be ignition noise or alternator noise >_>

What's confusing is the noise is fairly high frequency - in the 800-3000Hz range, which seems to match RPM fairly well (diesel car). So the noise frequency is about 50-60x the engine's rotational "frequency".

well if it's a diesel car it certainly isn't ignition noise ;p

seriously tho the alternator pulley is smaller than the crankshaft pulley and also the alternator has multiple poles and three phases so yeah that actually is reasonable

That makes sense I guess.