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2005 Mustang GT

I recently purchased a used 2005 Mustang GT, and it runs awesome. However there is a whining noise that is present anytime the engine is running, and is relative to the engine speed. I was able to pin-point it to the A/C compressor pulley, partly through observing the noise becoming more profound when I turn on the A/C and the compressor engages. The A/C works perfectly and blows ice cold, but there is just this annoying noise. Do you think it could be the belt, pulley, or compressor? My son and I purchased this car as a project, and so we’re up for the repair if there is any to be had.

Engaging the A/C puts a big load on the belt…Remove the serpentine belt and start the car. Noise gone? turn it off and turn ALL the pulley’s by hand and see if you can isolate the bad bearing. The idler, water pump and power steering pump are the prime suspects…

If it whines with the AC off and compressor disengaged, it’s not the compressor. It could be the pulley on the compressor, or maybe the idler pulley. They’ll make more noise when the AC is engaged because more stress is on them

OK I took the belt off and started the engine, and behold the noise was gone. I tried spinning the pullies by hand, and the only pulley that made any noise was the water pump. When spun by hand the water pump pulley makes a slight and faint sqeak of sorts, but maybe at speed and under tension this is the culprit.

While it’s possible, water pumps seldom whine because they do not use bearings. They use bushings instead and these are not prone to a noise like this.

You might try placing a fingertip on the back of the tensioner pulley in the center.
Try rotating the tensioner pulley by hand. You may feel a slight tick when you initially spin the tensioner by hand but you should feel nothing as it’s spinning.
If you feel any very faint ticks, etc. then the tensioner is likely faulty.

The same procedure would apply to the alternator and air compressor. Sometimes the power steering pumps can have a tendency to whine a bit but that’s nothing to worry about if it’s not excessive.