Is it normal for the unit's power supply to make a constant high-pitched buzzing/squealing sound when the unit is plugged in but not running? It goes away as soon as the LEDs are switched on. Unfortunately, this is the case with all 3 that I now have. However, I have only noticed this since I attached one to the bed and the socket is near the head of the bed.... I'm actually satisfied with the product, but it's just a very, very tedious feature.