I often try to get away from music for a couple of weeks before working on new ideas, this helps to keep my head clear from other influences but as soon as people hear it I get " that sounds like ......" Often artist I haven't heard in years or even artist that I have never heard.
Heavy metal rips of blues and classical music some rip of folk and others rip off oldies and long forgotten songs but all this just comes down to one thing. inspiration, At the end of the day music is just the molding of sounds and as such doesn't really belong to anyone. (lyrics not included)
The only way you can get a sound that no one has done before is to created your own instrument and even then you will be using the same modes and scales that have been used since music began so on that note I wouldn't let it worry you, keep creating music and that totally original song may fall into your lap if not just have fun with it because music creativity wont come to you if you try to force it