Gave the Quad a good cleaning... took the rear plates off, vacuumed the fan on right, cleaned exchange tubes on top and ash in bottom tray... But I am getting this ticking sound that is constant... sounds like an engine idling. Happens when the stove turns on and continues when the blowers come on. Once stove is running for awhile, it seems to go away. Any idea what this is? Not the auger. Not the fan blowers below. Sounds like that heat exchange fan behind the back plate on the right side.... Ideas? Do I need to do a deeper cleaning? I have never taken the back off the stove in three years of use. Am I missing something there to clean???