It sounds like the main belt. It's incorrect adjustment or just an old belt.
Usually, it's the most obvious problem. Here's a funny story about a Mercedes dealer. A guy has a new Mercedes with the IR key. It's a system where you place this module in a holder and a motor actuates to read it and it starts the car. There is no conventional 'key'. Well, it stopped working so he had it in the dealer. They went through 'everything'. They replaced the wiring harness, readers, etc. They couldn't figure it out so they gave him an option. They'd either give him a brand new car off the lot or, as luck had it, he could wait a week when a team from Germany would be there doing their rounds. Well, he chose to wait with a loaner car. The German team came, looked at the car and said that the motor that works the reader had simply died. This is something that is clearly audible when working.
A long story short, I have been working on my own cars and bikes for years after similar bad experiences with all sorts of brand dealers, both domestic and foreign. In my experience, it is rare to find a dealer, at least in the US, that has a passion about about cars rather than a need for profit. The dealers, though, tend to play on consumers' fears and paranoias. Usually that sudden squeal or strange click is just something simple. But we tend to think the worst and wonder if the engine is about to die.
