It happens only when heater/AC are on and only if I hit the gas and it hits 3500 RPM. Almost sounds like a street bike (crotch rocket) taking off from a start.
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2008 Lincoln MKZ Question: Engine makes loud whining noise when heater/AC is on
Answer #1Superbob May 31, 2011, 08:34Master
I think maybe the drive belt is slipping on the A/C compressor making the noise. A defective compressor, a worn belt or a failing belt tensioner could be causing the noise. See if it makes the noise in PARK gear with the engine revved up and the A/C on.
FYI: the A/C compressor is engaged during DEFROST as well as during A/C use.
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Replylwerbyj, May 31, 2011, 08:38Rookie
Yes it does it in park as well. And it does it when either the heater OR the AC is on. Sorry, I don't think I was very clear when I wrote that the first time.
Answer #2mamamia803 May 17, 2014, 04:53Rookie
Was this issue ever resolved? My son's '08 MKZ has the same problem, and a Ford Fusion Club website cites a similar condition. The dealer replaced the serpentine belt tensioner.