Ah what a relief, my concerns are now allayed! Thank you for posting this stuff.
Experienced the exact same with my A500 2010 (diy'ed last weekend) - new Gates Powergrip belt, tensioner and water pump. Was careful to tension correctly and locked the top and bottom beforehand- all running as it should this week passed (Daily whip) but noticed this 'whirring' when idling.
Thought it was the auxilliary belt tensioner on the way out, but afer changing that last night the sympton still persists! Guess I'll have to get used to it for the next 5 years.... Definitely going to try a different kit, then.
...Has anyone yet changed from Gates and seen the whirring disappear?! Big love!
When I fitted the new belt, water pump and idler, I was confident that would "cure" this noise, but it didn't. The noise was almost exactly the same but possibly very slightly quieter. After fitting the new belt I was running the engine with the belt guard off - I usually do this whenever I'm fitting a cam belt so I can be sure the new belt is "happy" and properly tensioned before fitting the belt guard. This meant the the aux belt (fan belt) was not fitted so I knew the noise was not due to the aux belt, alternator or aux belt idler. I immediately suspected I had a defective new water pump or idler so tried my listening stick and listening tube on them, but no, they were running super quiet! That was when I carefully went round the whole assembly with the stick and tube and found the noise was coming from the belt itself. Living in a big city, as I do, and taking public transport and walking a lot, gives me the chance to listen to other vehicles which use this engine and it seems some make the noise and some don't. I'd say roughly a third of them make the noise, but that's an unscientific sample. - just what I've noticed when out and about.
Regarding your last sentence, "has anyone yet changed from a Gates?" I haven't yet, mainly because my main source sells Gates belts and gives me a good discount. However I do intend to buy a Dayco next time I do this one if we still have the car. Maybe worth noting that the belt I removed was the original FIAT belt which had the teeth with the wee slit along the peak of the teeth. The gates belts have a more rounded profile without this slit. I queried this with Gates themselves and they replied it was all about copyright on the tooth shape and makes no difference to the belt in service as the force is transmitted through the base of the tooth where it merges with the main run of the belt, not the tooth itself. I'd wondered if the tooth shape made a difference to the noise but it would seem not and, in practice this would seem to be true as my noise is the same both before and after the belt was changed. True to say though that although very similar the noise is just very slightly different with the new belt fitted so maybe the tooth shape does make a slight difference? I still find it strange that some make the noise and others don't.
When we bought the car I mentioned to the sales person that I suspected it needed either a water pump or idler in an attempt to drive the price down a little - I was being a bit "cheeky" as I'd been watching this car for a number of weeks and stepped in when they knocked it down in price. His reply was that "they all do it" Which isn't true, and offered to let me listen to a Ford Ka which was in the workshop for a service as it sounded the same (the Ka used the same engine) Unfortunately when we went through the car was up on a ramp with the sump plug pulled to drain the oil so I didn't press him on it. I've also talked to people I know in the trade, particularly Kenny at our local Fiat indy, who all say, "Yes, some do it and others don't" Non of them could say what causes it though and all agreed it sounds like a bearing noise.
So, after all that, I'm very happy that it's just a characteristic of this engine but I'm mystified and frustrated as to why some do it and others don't. I wonder if the next one will be the same - We'll very likely be replacing Becky with one of the last of the £30 road tax Pandas if/when we have to.
Note. Some may know I've been expressing interest in the Dacia Spring as a possible replacement and, although not convinced about having an electric car as our main transport yet, the Spring would be ideal for Mrs J buzzing around the town and out to our boys south of the city. I've discovered what might be a bit of a hitch in that plan though, not to do with the car but the charger installation at home. We are lucky enough to have off road parking which makes home charging the obvious way to go - much cheaper to charge the vehicle that way but is an overnight procedure. However our house still has the original fused supply, not a circuit breaker anywhere. I'd been told by the dealer that installing a home charger for the vehicle would likely cost somewhere between £800 and £1,000 but a friend, who has looked into it in more depth than me, laughed at this and said that would be unlikely given the age of my house wiring and to expect it to cost considerably more. I'm going to inquire of my electricity supplier, who seems to do the installation? to get a better idea of likely costs, but another Panda makes a lot of sense at this time.