I agree with Poppaea, you should take it back to the store straight away.
Even if they do not have a replacement in stock you can at least register the fact with them and arrange for a direct replacement as soon as one becomes available.
Like Poppaea I too have been buying Sony products for more years than I care to remember and not once have I ever had a problem with a defect.
In fact in all the years of having Sony Walkmans, Discmans, hi-fi, televisions, computers and now eReaders, I have never had to have anything repaired or replaced. Guess I'm just lucky.