If you use a MDT task sequence in SCCM CB 1602, then windows will be installed on the D-drive. To get windows installed on the C-drive, then you should find the step called “Set variable for Drive Letter”
Change the setting from “False” to “True”. Click “Ok” to save the changes to the task sequence.
I know the in the description is says “Only applicable with ConfigMgr 2012 SP1”. But I have also seen this issue SCCM CB 1602.