Jandy LT has loud vibrations when exhaust fan turns on

Hello everyone. I have a Jandy LT heater on my pool. I recently replaced an ignitor and flame sensor, which fixed one problem thanks to this website.

This was the first time I had turned the heater on in a few months. Once it came on and the gas ignited, I noticed a loud vibration when the exhaust fan was engaged.

I suspect it is simply the fan bearings are beginning to go, but could there be another cause? I read something online about a switch of sorts causing similar problems so thought I would check with the experts. The vibrations occur only when the fan is going.

Thanks in advance.
 
Im not familiar with that heater, but as far as I know, standard sequence of operations for gas heaters/furnaces is inducer(exhaust) fan should be running before gas is lit. Are you sure the fan is kicking on after ignition or is it possible the vibration you're hearing is the burners firing or possibly something else loose in there?
 
Im not familiar with that heater, but as far as I know, standard sequence of operations for gas heaters/furnaces is inducer(exhaust) fan should be running before gas is lit. Are you sure the fan is kicking on after ignition or is it possible the vibration you're hearing is the burners firing or possibly something else loose in there?

Thanks for your response. You are correct. The actual sequence is the fan comes on to empty any stray gas that may be in the unit. Then the fan shuts down (or slows way down) and the gas ignites. Then once the ignition is on for a few seconds the fan again "comes on". Whenever the fan is running there is the vibration.
 
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