I suppose that narrows it down to either AC compressor or the alternator. Any idea how I would go about ruling one or the other out?
You can disagree but from my observations your opinion is inaccurate. One trip to the Advance website and I see the clutch listed by itself just like the complete compressor is for a 2001 Focus: Advance Auto Parts | Car & Truck Replacement Parts, Aftermarket Auto Parts, Performance Parts & Accessoriesit's the most common reason why most compressors get changed. Most will not sell the clutches separate
It does seem to do it only for a few seconds after I turn off the AC. I'm wondering if it's the AC or clutch/pulley now.If it does it when the a/c is off even if it's less pronounced then it's likely not the a/c unless it's the clutch bearing. But that's real easy to check by loosening the belt and spinning the clutch by hand. You should also check all your pulleys this way: idler, power steering, alternator, and water pump. Listen for noise and wiggle for play.
Yup I did and didn't hear anything. I do have some new info though to add since I've still been daily driving the car. The sound seems to occur as the idle hangs around 1100rpm and is 100% following the RPMs after it begins returning to idle off throttle. I've begun feeling it in the pedals when I'm coming to a stop namely the brake pedal and not so much the clutch. That part is kind of alarming to me. It's gotta be one helluva vibration to be feeling it as much as I am. It seems to also be worse on hot days which we've been getting a lot of in Utah these past few weeks.Still could be the AC pulley--that's always turning. Did you start and run the car without the serpentine belt installed?
I checked all of them with my wife being my helper this past weekend when I changed the serpentine belt. I can hear the groaning and vibration in every accessory to some degree but AC compressor housing and alternator are the loudest which is interesting considering they're on opposite sides of the belt drive.If it doesn't make the sound with serp belt off that narrows it down to a pulley driven item, use the throttle link to rev the engine while standing in front, you might be able to narrow it down further and if not, you can use the old screwdriver to ear trick or a mechanics stethoscope on the pulley driven units to hunt the noise down