Default Qi charger - keep getting "charger connected" beep

I'm trying out a new Qi charger. It seems to work OK, but every couple of minutes I get the beep sound telling me that the phone has been connected to a charger. I also have an NFC tag stuck on the charging pad, which I have programmed using Llama to put the phone into silent mode.

Has anyone else had this problem? Is there a way of at least silencing the "charging" sound?