I have a grinding/rattling sound coming from my car when I hit bumps going pretty fast or going up a hill or got a alot of ppl/weight in the car, it also does it sometimes if I'm accelerating fast. I have brought it into 3 places to fix the prob... I've have the catalyst converter and the heat shield replaced. Any suggestions for what the problem could be or anything else that should be checked out to maybe determine where these lovely sounds are coming from?