I had the same problem on my 06 GUIV 3.0L TD. Replaced the belt and the idler pulley and bearing (from repco, not the whole assy like Nissan sells) with no result. I then read the above and removed the shims inside the A/C clutch and it doesn't squeal anymore! Thanks Rodney for the tips.

Note: I had to use a puller (no, not Bigrig) to get the clutch off the compressor.

Cheers,

Steve