*** UPDATE ***
So, I brought my 2017 GLC300 to the dealership today after experiencing loud squealing brake noise and I have 2 things to share:
(1) They explained that MB brakes are designed to be used with moderate to heavy braking pressure, and there can be a transfer layer from the pads to the rotors that needs to be worn off with regular braking, otherwise some squealing noise can result. Also, this can be more noticeable in colder weather, which is what we experience here in Toronto.
(2) They still agreed to examine the brakes and ended up replacing all 4 pads and associated brake liners (in the brake shoes). What's interesting is that in the invoice, they printed the fact that this GLC300 brake squeal had MB technician tips #L142.10-P-064944 and #L142.10-P-065927 associated with the recommended repair to replace brake pads and liners. Even if this is an internal technician blog for tip sharing, or if this an official MB release, it tells us that this is a known issue with some type of corrective action.
No more squeal, but time will tell, especially as the weather gets colder, and dry again.