CalgaryPony

So I just had the car in to the dealer for an oil and filter change and I get it back and now when I accelerate at pretty low RPM's (manual tranny) the car makes a loud rattle and sounds like something is shaking violently from the rear of the car. Not that I would be driving in too high a gear but we're all lazy once in a while and don't downshift while making a turn or whatever and I know its not great for the engine but it didn't do it before I had the car in for an oil change what could they have done?