DA50 problem
 

Hi I have about 50 flights on my DA50 with a 23 x 8 bolly, Run in on mineral and now on synthetic opti 2, 80 to 1. I have had no probs with this engine but today I started the motor with a strange noise, almost like the spinner was loose. The motor runs fine but with this metalic rumble most niticable at idle.

After inspection all seems tight. Bearings feel fine. The noise can be replicated when the piston is at top dead centre. The motor is a 2 yrs old and supposed to have the updrated con rod. Could the conrod bearing be damaged?

Does anyone have any idea what could be the cause before I send it off?