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After three days going by without an e-mail response from SKF, I telephoned them to again ask if it is possible for a brand new SKF bearing to be as noisy as an 8 year old NSK bearing whose noise just started last month.

The CSR engineer doubted that a new SKF bearing that could be defectively manufactured or damaged while being installed would generate a high pitched squealing sound. He said that when the balls in bearings have been damaged by pressure from a press being improperly applied to the bearing during insertion, then the balls can acquire flats on them but the sound generated by a small ball with a flat rolling in a deep grooved raceway does not generate a high pitched squeal.

He said high pitched squeals tend to come from dry metal parts scraping across other dry metal parts, as would be the case from a bearing that had lost its lubricant and where all the balls had seized up and the high pitched sound would be generated by the frozen metal components scraping on each other.

But where we have a case where the bearing is not seized but spins freely as was the case with my old and new bearings, then it is unlikely that either bearing would be the source of the high pitched sound.

The mechanic at my Nissan dealership concluded last week after placing a long screwdriver between his ear and the different belt driven accessories, that my idler pulley was making the loudest noise compared with the alternator and AC. Maybe the loudest noise he heard was indeed coming from the idler pulley, but was the noise travelling up his screwdriver really the same high frequency airborne noise that I hear with my ears, or was it a different lower frequency noise? Or could that thin metal disk that forms the dust seal over the exposed side of the pulley be induced to vibrate like a loudspeaker and generate that high pitched metalic squeal even though nothing may be actually rubbing.

I don't regret changing an 8 year old idler tension pulley bearing that may not have needed replacement. I have bought another 8 years of reliability. But I do regret that there still appears to be an accessory attached to my drive belt (probably the alternator) with a noisy bearing or some other dragging metal part.

I suppose I could start by pulling my alternator apart.