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Hi everyone! I'm new to these forums so please forgive me if I've posted in the wrong place...

We've got a 2006 Mazda 3 2.3L. It recently started making this awful noise... See video, it's very noticeable.


The noise only happens when the blower is on (with AC either on OR off) and almost exclusively while idling. In this video, the blower is on and the AC is off. What the heck? I've tried a bunch of googling and I haven't found anything similar to this noise.

it definitely sounds like it's coming from the passenger side, low-ish down, sortof around where the AC belt is.

Any guesses?

Edited to add: in rewatching the video I noticed the serp belt slows down a lot right after the rattle. Wonder what it could be...
 

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The only thing I'd expect to be cycling like that is the AC compressor -- the serpentine slows because the engine load spikes with the AC clutch engagement. Even if the AC isn't "on", the AC engages with the defrost setting, to dehumidify the glass/cabin. I suspect removing/cutting the AC belt will confirm that it is indeed the AC compressor.

Edit: before hassling with the belt, you could also try to stick an automotive stethoscope (or any thin metal rod, really) under and against the AC compressor body (be careful about the pulley, of course). That chatter is bound to produce a vibration you can unmistakably hear/feel. Edit 2: In case you don't know, this doesn't necessarily mean you need a new AC compressor; I wonder if it's the sound of a slipping AC clutch, and I believe that's modular.
 
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