Furberry

Hi, this is my first post. I'm glad I've found this site Here is my problem. I bought an MZ-R700 just a month ago. I am pretty sure it might have been refurbished, as the deal was rather too good to be true ($150 Canadian). It worked fine for about one week, and then the unit began to shut itself off in the middle of play. At first it happend once, or twice a day. Now it happens all the time, every 2 or 3 minutes. I've checked the battery, and I've tried using a diff disk and a diff pair of headphones. There is a brief electrical *pop* sound in the headphones right before the unit shuts off. It happens both in normal and in Hold mode. The guys at the Sony store could not give any advice, and just told me that I could send it off to their repair centre. :| What should I do? Any help is apreciated. Thank you so much