If you unplug your charging cable from the phone before unpluging your charging brick from the wall outlet, then some "charge" may remain in the charging brick. Just remove the charging brick from the wall outlet first, wait about 3 seconds for the remaining "charge" to transfer from the charging brick to the phone, and then unplug your cable from the phone. By doing these, there is no remaining "charge" in your charging brick and it won't make that buzzing noise. That buzzing noise occurs on all of my other charging bricks as well (for samsung tablet, lenovo smartphone, oneplus 2). Of course, if the charging brick makes that noise, just plug your cable in the phone (without plugging your charging brick in the wall outlet) - this will transfer the remaining charge from it to the phone and the charging brick will stop making that noise.