Root is the way if you want to be sure. Root your device, then go and rename/delete the poweron.wav poweroff.wav files. There are some apps, but there is no guarantee it works with every phone/carrier. https://forums.androidcentral.com/e...tails?id=com.antweb.silentboot&token=hXkf1G9r claims Note 3 compatibility but I haven't tried it.