Pam asked ... Do I need to open the housing to dry the motor?    |    James asked ... Remove enterprise enrolment from an Asus Chromebook C523N?    |    tom schwartz asked ... Bosch maxx 6?    |    Noman asked ... Reverse light switch?    |    Suzie asked ... Stuck Feed dog?    |    Click here to ask your question

Natural gas water heater makes knocking sounds, what to do?

This is a State Industries, model Select, PR650NBRT natural gas 50 gal unit. Plenty of hot water, but it intermittently makes knocking sounds while it heats water. It's about 7 years old. What do I need to do to stop the noise? Thanks
Tom, December 2009