When a very large gong is rubbed at the right rate and pressure it hums and makes the most amazing sound. It can be heard miles away if the temple is constructed to reflect the sound of it. I remember one such temple called Wat Nong Bua in the northeastern province of Ubon Ratchathani. The gong was large like this one and could be heard at the other end of town! Enjoy the video - this girl does a great job of making the gong hum.
(Click HQ for high quality video (bigger file))
This temple is in Nakhon Si Thammarat in southern Thailand.