PJBrent

Hi, I'm a total newbie and this is my first post, and I apologise if this topic is covered elsewhere, please feel free to point me in the right direction. I've had my 300CRD Estate for a couple of years now. Its a 2006 model on a 56 plate, with 102,000 miles. I've had a few problems but all been resolved. However, it has now developed, and getting worse, a vibration which comes in at about 55mph and increases as speed rises. The only way I can describe it is that it feels like a wheel has a flat spot on it? Obviously this is not the case, but thats what it feels like. It seems to be in relation to road speed rather than engine speed, so hopefully nothing to do with the engine, which seems to be running fine. The car feels generally fine to drive, no play on the steering etc., but the vibration comes in at around 55mph. It does have a few knocking noises on bumpy roads, probably a suspension issue, but I'm told these cars are very prone to this? It still passed its MOT middle of last year tho with no issue's. I wonder if anybody could throw any light on what the vibration might be please?? Many thanks in advance. Peter.