gurgling behind the dash

[davidpertuz at mindspring.com]

Recently I started occasionally hearing a curious rustling noise coming from
behind my dashboard, sort of like as if there was a mouse back there. When
I determined that its occurrence was based on the heater valve being open,
I reliazed that it is due to air bubbles in the coolant in the heater circuit.

In November I replaced my radiator, and refilled and bled the system per the
FSM. I think I had the heater on when I did this, but I don't remember for
sure. Is this due to having bled the system with the heater valve shut (seems
most likely to me), or is there some other likely cause?

thanks,
David