Hi all,
I have a Mazda 3 2006 2.0L 120 000km and recently a sound started to come from the engine. Idle, it sounds like this: https://drive.google.com/file/d/0Bzf...it?usp=sharing, but when I accelerate it is way more noisy.

What could be the problem?

 

the idle appeared to be steady, the engine did not shake, from what you tell the sound gets worse as the rpm goes up.
I am thinking it could be a bad water pump.
I am thinking it could be an issue with the timing belt. That is less likely because the idle is steady.

But most likely it is the clutch bearing of the AC compressor. That is a guess, but an educated one. I had the clutch bearing on our '98 protege going bad. It made ugly noises but did not affect the way the engine runs.

Remove the belt and start the engine. Run it only for 2 minutes because the cooling is disabled. If the noise is gone you know the problem is with something that is driven by the belt.