Got an aquenon heater from this guy I bought my most recent tank from. Heater was new in the box, just threw it in sweeten the deal. Anyway since installing it I've noticed a popping sounds (about 8 to 10 times) every time it turns on. Tank is in my bedroom and its loud enough to wake me. This worries me as I certainly dont want it to shatter. Is this normal, maybe a break in thing? Can anyone relate?