thiru,
It is doubtful the sternal wires are causing the thumping problem. While sometimes they can cause problems, it is usually manifest externally by drainage, redness or infection.
However, it is important to figure out what is causing the thumping and making sure it is not any type of arrythmia occuring after your myocardial infarction. Holter or event monitoring would accomplish this.
good luck
Almost two years is a long time for a normal scar to cause pain... You mentioned your scar becoming thicker. I wonder if you have hypertrophic or keloid scarring. If a person is going to have bad scars, evidently the scars are going to be the worst in the chest area. You might want to see a dermatologist for a consult(or painful -- sorry -- steroid shots) or even a plastic surgeon. I had some sternal wires removed by a plastic surgeon because they were painful -- bumping up right under my skin. Also, sometimes people can get small incisional hernias. Good luck!