Long Distance Calls

I have been getting long distance calls lately where the phone rings, I answer, you can hear noise in the background, but no one says hello. I get about one a day now and it is always from the same number. I tried to do a trace on the call but the phone company could not tell me who the caller was. All they could say was that the call was from a cell phone. I have been looking at reverse cell phone look up sites on the internet and have decided I am going to see if they can give me some information on the caller. If it had only happened once, I would not worry, but it seems to be an ongoing problem and I need to find out who is doing this and hopefully, why?