Finally realised what my 'shock knock' noise is: it's the fuel cap outer door flapping about while the car is moving. Big relief. Does anyone else have this problem?

Got the garage to put the car up on their ramps to have a look and they tightened one of the clamps for the exhaust pipe on that side. But the suspension was tight.

The door is prevented from opening fully by the lock mechanism. But there's about 5mm play at the latch, which seems to have been bent at some point. Plus there is no rubber or other cushion on the inner side of the door to cushion the flap.

Best wishes, Colin