e34 1990 535i noisy auxiliary heater pump

My Aux Heat pump growls loudly when I request heat for the driver , but does not growl when I have only the passenger heat turned on . This is a relatively new aux heat pump, say two years old.
Do I need to buy another one? Thanks, Mark
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mark barron wrote:

Since there is only one aux pump but two solenoids, I'm guessing the problem is with the solenoid, not the pump. Try unplugging the pump's electrical connector and see if you still get the growling. Then try the reverse (pump connected slenoids disconnected).
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