2001 Chevy Impala

Is the car overheating? If so them it could be a sticking thermastat. When the get stuck they do not open all the way making the car heat higher. This can cause bubbles as it expands. Make sure the cooling system is full of coolant, except for the recovery tank, that should be about a half to a quarter full. If you fill it all the way any expansion will overfill it.