Depending on how much the heater has been used, you may just have carbon/soot built up on the exhaust fan blades. This can be remedied by removing the blower assembly and cleaning the exhaust fan blades. They are the set on top. If could also be a bearing as you suggest but I would check the fan blades first. Let me know if this doesn't fix the problem.
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Depending on how much the heater has been used, you may just have carbon/soot built up on the exhaust fan blades. This can be remedied by removing the blower assembly and cleaning the exhaust fan blades. They are the set on top. If could also be a bearing as you suggest but I would check the fan blades first. Let me know if this doesn't fix the problem.