I got a ********* UMC 202HD. USB powered audio interface. No microphone plugged in. Plugged headphones into headphone jack, faint high pitch whine at headphone volume set to zero(7 o'clock position) on audio interface. The high pitch whine gradually decrease and disappears at headphone volume set to middle(12 o'clock) on audio interface. High pitch whine returns at 1 o'clock and gradually gets louder with noise added in. Tried plugging into 3 USB ports on my laptop(on battery) and also my android phone, same problem. Is the high pitch whine at low volume a ground loop problem since it disappears at middle volume? If not what is the suspected cause of high pitch whine? Thanks.