Hey guys, this sound has started coming from my car and I'm unsure what it is. I took it to a garage and they replaced my fanbelt but it's still carrying on. It's a whistle/squealy sound, but more on the whistle side of things. I want to attach a video but it won't let me, unless people are willing to let me email it to them?

Initially it would do it when I start the car and then disappears when it warms up, however now it's practically constant and at any speed.

My knock sensor is due to be replaced but I don't know if it's related, the one time I took my car to the garage it didn't make this sound so they don't know which is highly frustrating. Any help with what it could be and potential costs?