Settlers Crossing HOA

i am absolutely horrified that i have now discovered RATS (not mice) RATS in my garage.  has anyone else had this problem?  i live on lariat trail.  where could they be coming from????? we have no open trash containers in our garage and are absolutely disgusted and apalled.  i have NEVER seen a RAT in my life until 4 days ago. this is a nice, clean neighborhood.  i'm confused.  let's put it this way:  many tears have been shed over this.  i've been putting poison out in the garage and they carry it off.  HELP!!!!