My 2012 octavia vrs 1z mt (stage 3 )has started with a strange sound at cold start when it on idle

when gets warm sound gets decreased  ,otherwise car runs,pulls absolutely fine revised timing chains , tensioner, v belt , clutch is working fine still i am not able to figure it out what kind of sound it is ,so need an advice &help .

1.8 TSI?

Yes sir

what engine code? They only made the vrs with the 2.0 tsi/tfsi in the UK.