Mechanical sound from the car when accelerating.

What is your question?

When I am accelerating beyond a certain speed (~50 miles), I am hearing a certain noise from the car. When I brake, for example when coming to a stop or light or driving at a slower speed, it stops (or I couldn't hear it). Initially, I could hear it from time to time, but yesterday, I could hear it continuously. I want to know if this is a routine things to happen for Hyundai Santa Fee (2005 model) and if so how to fix it, the cost of fixing etc. If not, any idea as to what could be wrong so that I can get a sense of what the machine shop would tell me and what could be a possible price range for the repair work. Thanks a lot for your advice.