'evening Baglady, hope all is well with you? Apologies, I can't remember if you've ever told us your name - or name you may be known by, other than Baglady - I'm not trying to encourage you to disclose here if you don't want too.
"Replaced everything on the aux pulley" So did you fit a new alternator and tensioner and aircon compressor and crankshaft pulley? I'm probably misunderstanding you because that would have cost a small fortune.
When we bought Becky she has a small whiney zizing noise which I was convinced was something like the aux belt tensioner or cam belt tensioner or maybe even water pump, I was convinced it was a bearing type noise. It was not a loud noise and the garage agreed it was there but said "they all do that" and refused to do anything about it. Because she was, by quite a long way, the best Panda I'd looked at we went ahead and bought her. Very soon after that I took the aux belt off and ran her with it disconnected but the noise was still there. As there was no record showing her cam belt had been done - she did have a complete stamped up service book though - a wee bit later I changed the cam belt, tensioner and water pump. After removing the engine mount and belt guards but before I removed the old parts I ran the engine with the guards removed and went round the components with my long screwdriver stuck in my ear and it was obvious that the water pump was a wee bit noisy so I thought "That's the source of the whiney, zizing noise then"!
After I'd built her back together with her new belt, pump, tensioner etc, I ran her again with the guards off just to make sure all was Ok before putting the guards back on and, damn it, the noise was still there but not so loud. I broke out my automotive stethoscope and went round all the components - water pump, tensioner, etc, etc, and couldn't hear the noise anywhere although, when I took the stethoscope earpieces out I could hear it no bother. Double checked the water pump with the stethoscope, but definitely quiet now with the new pump fitted. The old pump was a bit "gritty" when spun by hand. So next I got my "listening tube" and stuck it in my left ear and went all round the components again listening for it. You have to be very careful when doing this not to get the "business" end tangled up in the belt and sprockets! When ever I went near the tensioner I could faintly hear the noise and I was beginning to think I'd got a slightly duff tensioner when it dawned on me that as I withdrew the end of the listening tube the noise momentarily got louder? So I went back in with the end of the tube and started moving it around that area until I narrowed it down. The noise was/is loudest if you hover the end of the tube over where the belt feeds into the cam sprocket, right where the belt's teeth engage with the sprocket teeth. I investigated this for several minutes and I'm in absolutely no doubt that there's some sort of quiet "siren" effect being produced by the belt teeth as they engage with the cam pulley. She's still doing it exactly the same today, that's a couple of years on. I've listened to others with this engine and some do it and some don't! My boy's Punto, for instance does it so quietly you can only hear it if you really know what you're listening for - he doesn't hear it. It annoys me slightly and when I next do a belt on her I'm going to fit a genuine Fiat belt rather than a Gates (my preferred brand) just to see if it makes any difference.
When I did Becky's cam belt and also, but not so much, on my boy's Punto, there was a fair collection of detritus around that bottom cam belt pulley/sprocket (I tend to think of a "V" or "Multi V" belt running on a Pulley but a toothed belt running on a sprocket?) Here's a pic I took of Becky's at the time:
View attachment 217993
I think that this belt was the original and that would seem to be supported by the small cracks you can see in this picture but also notice that the teeth of the belt are not a snug fit to the teeth of the sprocket - albeit I had slackened the tensioner before I snapped this pic, but you can still see there is clearance on the sides of the teeth which will have worked wonders for the cam timing?
Doing your first cam belt is quite a stressful experience, especially if your engine is the interference type - which, being a 500, it will be? Have you read Andy Monty's guide in the Punto section? It gives you absolute chapter and verse on doing one. You'll need to look at the add on he did for the VVT pulley. If at all "nervous" about doing it I wouldn't try to talk you into it though. Have you discovered a "nice wee garage" yet? Just maybe they would let you watch - and maybe not.
I think you told us previously where you are, but I've forgotten - surprise surprise! - If one of our more able members is somewhere near you maybe they could help if you want to give it a go?
Whatever you decide, good luck! and I'm sure you'll keep us up to date as you have previously.