2009 2L diesel just gone over 100k. This has just started, at full lock the steering wheel jumps a little and there is a knock from under the bonnet - my guess is its the pump relief valve operating. It's worse when cold and also some times when turning the wheel when manoeuvring the wheel jumps, bit like there is air in the system. The pump was replaced at about 15k under warranty. I checked the level and it was low so have topped up the reservoir but no improvement. Any ideas?