noise from timing or exhaust

[Redbike]

Hi
I have an Yaris 1.0-2003 five door (update model 65Le)
Now 70000km and carefull driving and service.
However now the second winter, when only under 10C outside
I always can hear some metalic noise from the engine room.
It comes only around 1600-1800RPM.
When the weather is colder it comes to be louder.
But I can not hear it in warmer condition or when I try to rev up the motor in neutral gearshift.
I wisited the dealer service, but they did not help me.
They only told me, it may come from the exhaust silencer.
Yes, it would be the best, so I can drive the car more.
The silencer was checked and it is tight. Maybe inside some lamella is partly loose or vibrates???
However some mechanic told me, it can come from the timing chain system. From the hidraulic timer.
It can be used for now.
I always use the Shell Helix Ultra 5W40 oil.
I have to drive the car 1 hour in the city then the noise is off (more or less)
Has anybody idea or experiences, what can it be?
thanks
Peter

-I don't like when a Toyota has a noise like this-:confused:

[Redbike]

this 5W40 full synt oil is the standard. however 10W40 cheaper oil could be used too- but I always use 5W40 Shell.