I have a freelander T D 4 es auto diesel , 2 litre on a 51 plate . and my problem is that it has started to make a single thump , ( under car not engine), it seems to happen intermittently when going up the gears and the car is travelling at 30 mph., at around 1500 - 2000 revs in normal conditions, any help will be appreciated , thankyou in advance steve(sr151)