My Kenmore dryer heats initially then stops. I took the front panel off and watched what was happening. The coil heats up, and then then flame ignites. After about 3-5 mins., the flame goes off, the heating coil glows, but the flame will not re-ignite. The area seems to make a rattling noise as he flame tries to re-ignite. I have reas that this may be a gas valve assemby problem or a gas valve coil problem. Is this true? If so, how do I check?