Okella

I have similar issue with my Octavia 1.6 TDI 65 Reg, the chirping sound coming out from the engine and goes away after driving the car for a while but i noticed it only happens during cold weather and when the car is idle and not moving. When I got it checked by a mechanic, he thought it was to do with the tensioner + belt so replaced both but the sound still there. The mechanic is now suggesting to change the time-belt + water-pump after diagnosing the car for several hours, he thinks the sound is coming out from the side where the time-belt is located. The car has only done 40K not sure if changing the time belt would eliminate the sound. Any idea what the reason for the sound?