when driving my XLR i knowest a loud Knock in my engine on 2004 Cadillac XLR

i knowest it when im seating at a taffic light on just seating in the car< what could that mean

by in District Heights, MD on December 28, 2012
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1 answer
ANSWER by , December 28, 2012
a knock in your engine is not good, have a mechanic look at it right away