For about six months now, my hot water tank has been making loud noises whenever a hot faucet is turned on. The sound is not in the pipes, it's in the hot water tank. It makes a loud clunking sound and also when the gas burner is on to heat the tank and someone uses hot water, the tank makes a loud bubbling sound. I thought it was air in the tank or pipes, but I can't seem to get any air our of the faucets or out through the pressure release. I've also tried to drain some water out of the tank, but nothing has helped.