Why is the ford focus making a rattling noise when accelerating?

The Ford Focus, like all automobiles, is made up of thousands of individual parts that are bolted, clamped or pressed together. Combine that with the very rough daily experience of being driven and You have an almost unlimited source of rattles or any other noise You can think of. The most common source in the Focus is going to be Your exhauSTSystem. Once the car gets a few years worth of mileage the exhauSTSystem starts to wear and fasteners start to loosen leading exhaust leaks and rattles when accelerating. Another source could be the valves, when the car is run with low oil, the uppermost parts or the most likely to receive damage. In this case that would be the valves, they will make a chattering sound that will increase and decrease with the engine rpms.