I can only redirect you to U.S. Copyright Office -
http://copyright.gov/, for we are not lawyers here, and non-professional answer may only entangle the matter.
And my own opinion : I think that first of all better to decide if you're in need to move... It can be that similar melodies are performed by several artists, but what human rights are really infringed by this? Or it's just a marketing strategy to gain popularity via another copyright scandal... What can really infringe one's rights? Basical rights - like a right to be, to live & to breathe? Definitely not using the same melody you've "gave birth to". And let's try to look at it from such point of view - some people say that single information field exists, and all information blocks can be accessed by any person from any place if only this person can hear an answer to its questions... Than what originality can we speak of? Just like a right of first discoverer of something that has ever existed. It's another if applied to material objects - like pictures or sculptures. But I think that information is a common thing and can not be a property.
Music copyrights Limitations
Linear Mode
