So recently I purchased the IPV2 from a local vape shop. It works flawlessly and does not have any visible quality control issues that they are starting to be known for. This being said, occasionally when i charge it, there is a very quiet, high pitched noise. It kinda sounds like a very tiny kettle coming to a boil. When this happens, i unplug the device and the noise stops. Like i said it doesn't happen all the time but its a little worrying. Anyone have any explanation? Thank you.