I recently had a snapped aux (alternator and a/c compressor) drive belt, which I have replaced, but I have since noticed a horrible rattling noise at idle and slightly above idle when accelerating, but which disappears at higher revs. The noise started only after fitting the new belt, and I saw a post on another site that suggested the tensioner could be the cause of the rattle noise (maybe a bad bearing?), but I want to make sure I know what is causing the noise before spending out more money on parts or going on a wild goose chase. My thought initially was that it sounded like a loose heat shield, but it seems too much of a coincidence that the noise has only started since this issue (snapped belt) happened.

Any ideas / suggestions would be much appreciated.

Thanks, John

 

The tensioner pulley may have been the cause of the belt failure. I'd suggest taking the belt off and rotating the pully by hand to see what it feels like. Should rotate smoothly. Also spin any other component driven by the belt. You can start and run the engine with the belt off to help diagnose the problem just don't run it too long a couple of minutes should be fine. Post back what you find.

 

Thanks Charles, I'm pretty sure that before I fitted the new belt I did manually spin each of the pulleys (aircon, alternator, sprung tensioner, static tensioner (I think that is what it is - it located at the bottom and is turned by the flat side of the belt)) and I didn't notice any of them being rough/wobbly or stuck, but I suppose if it is just a worn bearing it may not show up with just a few turns. What I'm thinking of trying, is removing the belt and then using a drill or my dremel style tool with a rubber wheel in the chuck so I can use it to spin each pulley up to a fast speed where the roughness / noise might show up.

 

Yea i'd go over it again it's probably a simple fix. You can listen by using a long screwdriver against your ear but use caution near moving parts.

 

no need to put yourself in harms way…

See post #3

https://www.mazdaforum.com/forum/maz...icopter-55445/

 

These are really good tools for locating noises.

 

You will need to safely listen to all pulleys, My 2 cents would be AC compressor &/or clutch.

 

Yes there are but the one is problematic. We have one similar but seldom perhaps only used it the day we got it for the shop. The owner thought it would be great to have because FORD actually has one that is similar, but you would be hard pressed now to find many if any FORD dealerships using them. This tool picks up and reports to many sounds and the echo effect which causes longer diagnostic time to isolate the sound origin.
But hey,....... if you personally have experience using this one you posted then you likely know the challenges using it.

 

Don't know any more than what Amazon says. Only a suggestion. I have made my own and no BS you can hear white ants munching in timber.

 

well this explains a lot of some of your response, possibly the results of the 70s acid trips . 🤪