Audiovox SMT 5600 / SPV C500 (HTC Typhoon)

I need to know soon if I should replace my new 5600. My wife says sometimes (not always) when I'm talking to her on my phone she hears this noise like a tea kettle whining really high pitched. It continues to get higher until it disappears. If I listen real hard I can hear it too. It's not that bad, but if it's something out of the ordinary I'd like to get it replaced.
Anyone else have this sort of problem? Should I get it replaced? I'd hate to be without a phone for 2 weeks or more, but I don't want a bum phone. Please give me advice!!! 🙂

Thanks, -BL