Clunking noise

When I pull my car away after starting the engine in the morning, there is a subtle clunking noise coming from around the boot area.

However during the rest of the day, no such noise is observed for subsequent starts and pulling away of it.

There is also no/very little luggage in the boot on an average day.

The car has been well looked after with no history of having gone over pot holes, hard braking or handling to date. I have been the sole user and it has never been overloaded with either passengers etc.

Any advice is appreciated.