Does anyone with a tesco phone get cut off after about ten mins with a loud deep noise?

I have the adaptor set up - and it still doesn't seem to work (think I mentioned this further up the thread) but its so frustrating when it seems everyone else can use this service and i can't

I can call out and receive calls but i can't have a call that lasts longer than a few minutes - the quality is good while I am on the call but then all of a sudden this loud noise appears so i have to hang up, when i i go to make a call again on it the loud noise is still there so i have to wait several hours or even a day before I can use it again