I just bought a 2004 Honda Jazz Manual. When I make a turn it squeals?

I just bought a 2004 Honda Jazz Manual. When I make a turn it squeals. When I switch the air con off the squeal stops but sometimes it goes away when I change gear even if the air con is switched on. The squeal lasts about 5 to 8 seconds depending on whether I change gears, switch the aircon off or restart the engine. Does anyone know what the problem is here? I'm guessing it could be the serpentine belt.

Those symptoms are perfectly classic for belts, and at 10 years old it is due anyway. Don't try to retension an old belt and don't put anything on it, just get it replaced.