I recently replaced all the idler pulley's on my VS with Holden parts.

-The new tensioner pulley is metal (works fine)
-The idler directly below the coil pack is identical to the one that came of it (works fine)
-The A/C idler is metal and included a washer as a spacer so that the metal guard does not hit the pulley

I fitted the pulley's checking there was no contact with the metal guards, but when I started the engine it started making a noticable screech. I narrowed the problem to the A/C idler pulley and went to Holden and they replaced it, even though there didn't seem to be much wrong with it. The replacement bearing felt exactly the same, and when I put the new one on and there was no difference.

Next I went to the mechanic to check I wasn't being an idiot, and it turns out that the noise is indeed coming from the A/C idler pulley. He is not sure exactly what the problem is, but said that he has heard similar noises before from VT's.

The A/C idler pulley does not mount as firmly as I would like, but I can't work out how to stop this. The mounting is new, cause I buggered the old one getting the old pulley off, so it shouldn't be worn.

Is the mounting the problem, or have I got two dud pulley's in a row?
Any other ideas?
Has anyone else experienced anything similar?