In the past month or so, the cooling unit has a whistling noise, when it is cooling the air. The noise seems to be in the area where the air filter is. The filter has been changed, but it didnt make any difference. I went outside to hear how the unit sounded, it seems as if, something that is turning might be off balance
or in need of lubrication. Any suggestions or information will be greatly appreciated. Thank you! :rolleyes:

Lennox high-efficiency heating and cooling unit : CHP20V: 12:00 to 12.60 seer }
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It could be many things. You might see if the outdoor motor can be lubricated. You might also check the access panel's are installed correctly not allowing air to by pass and cause the noise. Also check the motor shaft by moving side to side and pulling up and down on the fan blade. If it is to loose it could also be a problem. NOTE turn the power off before checking.