No worries, I'v asked as heard that when some issue with timing belts etc might cause increase fuel consumption but here there is no such case

Finally was able to get my c-class for dealer diagnose... It took them some time including 1:1 comparison of the same engine models and the resulted of turbine actuator replacement under the extended warranty.
Now engine sound is much better, however the 'whistle ish sound as they confirmed is normal for those models.

Glad to hear it is back to normal OP.