We just finished replacing timing belt on brm head. Motor was running bad before. The ck engine light codes reveled problem with egr system. We replaced egr valve and pipe that has dash pot valve on it. Then we replaced timing belt. The motor seamed to run fine after a while but then would run bad. not sure if cam is bad or other. After replacing first mentioned items. car runs stronger. however it seams like it has a bad nock sound. like when you gey bad gas. And it seems to have a louder metallic sound which it did not have before timing belt reolacement. Any sugesstions?