the thing that generate this external interference can be synchronised in another place (on a GSM network i mean) in that case TA=16 doesn’t mean that the issue is at 16*0,55 km it means that it seems to come from a fix point. If you’have real interference with another cell with same BSIC,BCCH you can see the same behavior on TA but all cause are seen (LU, Page response, LMU, …).
I agree that it could come from BTS itself that’s why BCCH change should tell us more