if it is a bad knock then pump timing probably out. will cause imbalance to engine and probably wear engine eventually. hard to say if it will damage quickly or not. perhaps garage should sort it out for you if noise only appeared when you picked it up.
me
June 2009
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.