BB Bold :: 9790 No Sound On Outgoing And Incoming Calls?

I recently picked up a 9790 from Telus and I have noticed that it is randomly losing sound on outgoing and incoming calls. With outgoing calls it dials out fine and connects to who I am calling but I don't hear the ringing when the call goes out and I can't hear the person on the other end when it connects. When I receive a call I hear my ringtone but when I answer it I can't hear the person on the other end.The only way I can talk to someone when it is acting like this is to switch from headset mode to speaker.I played around with my phone and sound but could not find a fix. The only thing that works is a battery pull but even that is only temporary. So far the longest I can go is two days before I have to do another pull.

Any ideas on what could be wrong or should I just take the phone back and get a new one? I've heard this is actually an issue with the 9790 so I am a bit worried about replacing it when it could happen again.