Okay i have gather enough evidence to say with confidence that there is always a mob
spawner near i cant tell you where to look but walk around your spawner you may have
to put it on easy or normal or something so you can here them the type of spawner is
totally random or you could just do Vortexel idea to help you find it i have found 
every type of spawner Monster spawner that is it really helps hope that helps if you 
havnt read Vortexel idea look him up he has some good ways to find them.