Good day, it's a 20 years town house and I can hear popping or cracking noise whenever I turn or AC or heater. I only hear when I am at 2nd floor. I can hear when I am at living area, but it's coming from 2nd floor. don't really hear at basement. When not use the furnace, it's pretty quiet and can only hear the noise when the furnace it on, which the fan is running. The noise is like something popping or racking inside of drywall, somewhere close to ceiling area. The noise is much louder and clear when I am at master room compared to 2 small rooms. A local handyman came out, took a look told me nothing wrong in house, since it is a winter time, turn the heater on and humidity is low, expand and shrink down the drywall and joint could make a noise. Any advise please. Thanks.

Situation; Rheem Imperial 90 Plus The igniter was bad on this furnace. Measured resistance was 470 ohms instead of 46 ohms of a new unit. When I watched the furnace go thru the start up sequence with the 'bad' igniter (that barely glowed), I couldn't tell if the 'clicks' were a relay to lit the igniter or the gas valve opening. If it was the valve opening, the gas never lit, but the sequence continued and started the blower anyway with no flame which I didn't understand. I was under the assumption that would [B]not[/B] happen with no flame. Am I correct here? Previously, I have changed out the PCB's a year ago due to the original boards (I have two identical furnaces in the 'double' I live) having a bad design causing 4 resistors to 'fry', though the furnaces still worked. The replacement was a completely different design no doubt due to the 'poor' design of the original. I don't know if that is/was a factor not with the blower being allowed to run with no flame. With the new igniter (the 2nd replacement since the furnaces were installed Nov. 1994) the system runs fine as expected. I was just concerned about this, what I thought was a 'odd' behavior. Input?