Strange noise after ignition and few meters drive on a Toyota azt250

I have just bought an old 2003 toyota avensis (azt250 2.0 petrol d4-vvti engine, about 150k km ) and getting a strange noise that I cannot understand.

The noise is a kind of gear engaging “clunk”, seemingly somewhere under the front chassis (hard to spot). It happens only once after engine ignition , and after having moved the car for a few meters (about 3 meters). It is also very reproducible, happens after each engine start, but never before having moved a bit.

The car also has intermittent rough-idle+stalling problems, not sure it is related. I am going to change a bad o2 sensor, hopefully it will resolve this last issue.

any clue would be greatly welcome, thanks.