Lawmakers on Capitol Hill are digging into the question of whether Fannie Mae and Freddie Mac charge too much for their mortgage-backed securities guaranties, and the issue could be taken up in efforts to revise regulatory oversight of the two government-sponsored enterprises. In hearings last year, several lawmakers questioned whether GSE guarantee fees were too high. This fall, the Office of Federal Housing Enterprise Oversight quietly sent its analysis of so-called G-fees to Rep. Richard…