First: zr/dogo (c5502/c5503) has a 2nd mic...
However, on all custom roms, it's not present/detected at all, it can be tested via recording video, then covering the main microphone. Normally, with stock rom, there'll still be sound, but on custom rom because 2nd mic is not working, there will be no sound.
The issue has been reported separately here:
And mentioned numerous times in xda's zr forums.
The solution, currently, is to return to stock.
Note that this is not the same problem as troubled recording sound in stock roms, like this...