Default Sound cutting out whilst on a call?

Got to say i don't make many phone calls so i have no idea when this issues started but here it is...

When i make a phone call the sound cuts out intermittently. It's almost like someone presses a mute button for half a second or so. So i miss maybe one or two words the caller says. They can hear me fine the whole time the issue is just on my end and it is over speaker and regular calls.

I have restored to factory image and it is the same. On the Three UK network.

Was thinking of maybe trying a different sim card to see if thats any better but it's a pain to test. Has anyone got this issue or got any ideas on what it could be?!
Very hungry. I want Gingerbread.

Join GiffGaff and earn Payback yourself. The mobile network run by YOU.