Makes clatterin noise when you give it gas

I have a 2000 V6 Mustang with 166000 miles. When I accelerate (give it gas) it makes a horrible clattering sound. Its been doing this for a few years but it was not as loud or as constant as it is now. When I first heard it a few years ago I had a tune up, they cleaned out the fuel system and I started using better gas but it still did not help. Since it has gotten worse I took it in and they just changed the fuel filter. The first time I took it in the guy said if those things didn't help then I would need a new fuel injector. What does it sound like to you? Also lately when I go to stop the car seems to be kind of bumpy or surge a little.