So as far as I know i was going into the bunker aka "Super mutant bunker / between Museum of Technology and Museum of History", Cleared both of the super mutants and preceded to the other entry. When all of a sudden I hear a ringing like an older telephone, I frantically run around trying to locate the source of the ring but could not find its source, what i heard next sounded like the caller gave up or as if someone picked up the phone, then silence. I am pretty sure it was from the game as it faded in and out depending on how far i was from what sounded like the source area of the ring. Has anyone else experienced this? or know of the origin? or if it's even in the game!

No Mods, No Expansion packs, just straight up Fallout 3 (Fully patched).