Since the "big freeze" in December our Mazda 5 (diesel) has developed a squeak that's continuous for the first few minutes of running. It seems worse when the weather's damp but I checked the aux drive belt on Sunday and it seemed quite tight. There's also no slip on the alternator (none that I could force with my fingers anyway).

Someone suggested to me that the clutch release bearing might be the cause so I tried dipping the clutch and while the tone changes with the clutch dipped, the noise continues whether the clutch is up or down.

The noise is quite piercing but, to be honest, it doesn't sound like the belt slipping (it doesn't squeal more when revving the engine, like belts usually do when slipping).

Has anyone else experienced this? (or have any ideas of how to narrow down the cause)?

Many thanks for your suggestions...

 

Have you tried spraying belt dressing on the belt? If that doesn't stop the noise, then chances are you are correct about it not being the belt.