MY 2.7L 5M makes rattling noise (like worn idler pulley bearing) when A/C is on and clutch engages (in neutral). Once clutch pedal is depressed, the noise is gone.

I try to replicate the problem by raise the RPM with no A/C and clutch engaged (in neutral) but no noise. I am unable to troubleshoot in gear since road noise is much greater than bearing noise.

So, what kind of noise am I hearing?