I got a 2002 cavalier and i just took out the plastic air resvoir for the intake and the plastic protector on the wheel well. The same day i got caught in a bad storm and drove through some deep water. On that same trip home, there became a loud thumping noise under my front wheel, the same as the one i pulled the plastic out of. I don't know if a bearing lost its grease in the water or if plastic is vibrating since i pulled out the extra stuff. in any case, it does not sound like metal to metal and it only occurs when i am going straight. If i accelerate, brake, or turn, it goes away completely.

Well my guess would be something is either out of grease like tie rod end or ball joint, maybe you got a mount worn,

Did you run over an animal?