dumbblonde

I have a loud noise coming from somewhere in my car. It doesn't do it all the time but it sounds like a very loud squeeking noise. I can here it when I go slowly and also at times when I turn and or brake. Two mechanics have said they didn't find a thing but I am afraid the car will come apart on the freeway.

I was quoted $550.00 to replace the coolant housing, oxygen sensor and the engine light diagnostic test.Is that high? This is through a regular shop, not a dealer.