We have 22K miles on our 2018 CX5. Recently noticed a very soft knock sound coming from the engine bay when the heater is on. Goes off as soon as I completely turn off the climate control system. Sound only happens once a month and then goes away. Heater and AC seem to work fine. Sound is so soft can only hear it when car is not moving or moving less than 5 MPH.
Any ideas?
Any ideas?