I suspect that a being's power has an effect on their 'volume'. Mara being a class 1 is far louder that Megumi.
Additionally, I would assume that Megumi's personal tune blends into the backgroud music much better than Mara's.
Finally, Mara wasn't expecting to run into any of Heaven's agents except Chris and the Norns (and maybe Peorth). It's possible that she would have sensed and reacted had she heard one of their songs.__________________
666-HELL The phone number of the Beast
___________________________
"I've always wanted to be somebody, but I should have been more specific." - George Carlin
Additionally, I would assume that Megumi's personal tune blends into the backgroud music much better than Mara's.
Finally, Mara wasn't expecting to run into any of Heaven's agents except Chris and the Norns (and maybe Peorth). It's possible that she would have sensed and reacted had she heard one of their songs.__________________
666-HELL The phone number of the Beast
___________________________
"I've always wanted to be somebody, but I should have been more specific." - George Carlin