common knocks are front centre anti-roll- bar bushes and front lower arm rear bushes. take off your wheel and look at the lower suspension arm. there are 2 bushes in the sub frame, look to see if they are perished or split. as for the anti roll bar bushes visually check to see if the inner part of the bus looks a rusty colour, or get under and give the roll bar a good tug to check for movement.
if these items havent been replaced before, they deffinately will soon! SO COMMON!!!