I have a 2008 Focus Titanium Auto 1.6. It’s done 45,000 miles and in all other respects is fine. After starting the engine and pulling away I get a loud clunk noise after its shifts from first to second. The sound can happen before or after the actual gear change and only happens the first time after starting the car.

Each successive gear change is fine and no power loss is ever felt. If the engine is revved higher the sound is considerably quieter than at low revs - but still happens none the less. There is no variation with temperature as the noise happens if the car has been running and then re-started - or from cold. Any ideas what the problem could be?