Just unpacked and installed my new LaserJet Pro MFP M130nw I bought on Amazon. It works, connects to WiFi and shows no error messages but it makes a very high pitched whistling noise when it goes to sleep mode. It comes from the area around the power input. The printer is plugged directly into a wall outlet and I've already tried different outlets around the house, installed the latest firmware version but it did no good. The noise is very annoying in itself but what makes me really mad is that HP have known about this problem for several years and many people are still reporting the same issue repeatedly.