I have a 2005 V6 Mustang with 46,000 miles. I have just realized that when I slowly accelerate and it goes up to 1.5-2 rpms you hear this knocking noise, Like its changing gears hard. I take good care of my car so I am not sure why it is doing this.What should I do? I am suppose to take it into a dealership tom. and let them look at the engine, I just don't want them to charge me and arm and a leg to fix it.Any suggestions?