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      02-18-2020, 07:11 PM   #12
Ilma
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Canada
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Drives: 2008 135i
Join Date: Nov 2008
Location: Mississauga

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The humming noise sounds like the boost control solenoids bleeding air. They are located just behind the coolant tank, so that's where the noise is probably coming from - not the coolant tank.

Would be a good idea to replace them soon. Not expensive and not hard to diy.
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