I have a 2000 cavalier and recently i have noticed then when i drive there is a lound thudding/grinding noise comming somewhere from the front the car. It is very noticeable going around 45-50 mph. Would anyone have any idea what it could be ?  thanks 
Jen
 
i dont know about the thudding but i heard a rubbing noise when i drove fast a while ago and it turned out to be the wheel berrings
 
Also, you might want to check your cv joints.  One of them might be gone.
