unusual beeping noise during call

[jaymdee]

has any one else noticed a beep after a minute during a call.
this only started happening after the 2.1 update. the beep sounds like i am getting another call. also phone calls seem to be draining battery rather fast lately, a three minute phone call will drop my battery from half to yellow

 

[DECGTC]

I have heard this beep when using Google Voice but that's the only time...