ticking from torque converter
 

hi everyone. car is 97 e320, 140k miles with the 722.6 transsmision. for a while now, sometimes in cold starts i hear this little ticking from underneath the car. you have to concentrate in order to listen to it. at first i thought it was coming from the engine, an oil lifter or maybe the air pump. i had my mechanic listen to it and he traced the noise from the torque converter, but everything looked fine there, no leaks and he tightened the bolts more to see if the noise would go away. the car shifts and drives smooth like it did 10 years ago, no codes, everything seems good.
what do you guys think, what could this be???:confused: