Moonraker hi, what's the mileage ?
could it be UCA time
....... without a load on board mine went " crunch " quite a few years back up in the Italian Dolomites ....... stopped, investigated and nowt seemed an issue .... got back and some months later she failed on the UCA that side .... guessed it was that at the time ... made zero difference to the driving of the car at all ...........
OR
it could be a loose exhaust shield . one of mine just loosened a fraction and made cruchy noises on one specific not so local speed bump configuration ..... after happening a few times and only at that location and over many months, and after investigating further, the offending shield was surgically removed . only one bolt holding it back from dropping off it seemed
Doubt it's anything too serious to worry about ... it's a Ls400 with sometimes self-healing capabilities
Malc