your right but I've learnt from this thread. I have struggled with a whining noise since the engine went back in, looking all over for bearing problem, but perhaps it was the belt. Weirdly, changing back to a Fiat OEM tensioner reduced the noise but I was still getting whining when hot. After reading this, I've set the belt tension with the engine hot, presume this has loosened it a touch - hey presto no whine
This thread, and particularly your post here jonti, has set me to thinking about the wee noise which Becky makes. I've mentioned this a couple of times elsewhere but so people will know what I'm talking about here's what I've found.
When we bought her she had a slight whiney noise which sounded rather like a tensioner or water pump bearing in the very early stages of failure. The garage we bought her from said "a lot of them sound like that, the Ford Ka does it too which has the same engine" and refused to investigate. The rest of the car was in much better condition than others we'd looked and she is a Dynamic Eco, which is a spec that particularly interested me, so I bought her.
Within a week of getting her home I ran her with the aux belt removed but she still made the noise so, as there was no record of a cam belt having been changed I put a complete belt, tensioner and waterpump kit on her. In fact I think, at just under 60,000 miles and around 6/7 years old, the belt was the original! The old tensioner felt absolutely fine but the waterpump was just a little rough when spun by hand so I concluded it was the waterpump making the wee noise.
How wrong I was. The exact same noise was still there, although somewhat quieter with the new belt. I spent quite some time going around with my mechanic's stethoscope and my listening tube, with the engine running, trying to isolate where the noise was coming from. The stethoscope, which, for those familiar with the technique, works on the same principle as sticking a screwdriver in your ear, was totally inconclusive. Changing to my listening tube and moving the open end around the whole run of the belt it quickly became apparent the noise was coming from the top end of the engine. The only component which made "sense" to me was the tensioner, but it was quiet when checked with the stethoscope - very strange! Then I realized the noise got louder when the end of the tube got near the camshaft sprocket. So I started, very carefully and slowly, moving the tube end around that area. After a lot of careful moving the tube around it was obvious the noise was coming from where the belt teeth were feeding into the teeth on the top sprocket. I minutely examined both the belt (Gates, my favourite brand) and sprocket teeth - both looked absolutely fine. On restarting it sounded exactly the same and has continued to make this slight noise ever since, if anything it got slightly louder once the belt had settled in. Mrs J doesn't hear it even when I stand her beside the car and tell her what to listen for!
I've noticed some, but by no means a majority, of Pandas I've heard out in the street doing it also - seems to be a lottery whether your car does it or not.
Of course, being a 2010 car, our Panda has a spring loaded automatic tensioner so it wouldn't be so easy to slightly reduce belt tension - I'd be worried that I might reduce it too much and risk the belt being able to pull against the spring enough to let it jump some teeth. However I think that it's possible the auto tensioner is holding the belt tightness at just the threshold of "belt whine" which would explain why some seem to do it and some don't?
On the other hand she's run absolutely fine like this for some 3 years now - and presumably ran like that with the old belt since new - so I've decided I'll just live with it - After all, I seem to be the only one in the whole family who even hears it!