I recently drained and refilled the boiler with 400 gallons of tap water and Chemworld Wood Boiler anticorrosion chemical. I had to weld some leaks on it due to firebox acid corrosion. I have a Taco 007 cast iron pump. I started the pump with cold water and everything quieted down after purging air and securing the pump for vibration. I added 2 quarts of Hercules boiler Liquid Stop Leak to 400 gallons of boiler water. I shut off the valves and pump in the middle of adding it. I then heated it up to 180 degrees and opened the valves and turned back on the pump. There is a drip leg coming out of the boiler to help keep particles from entering the pump. The pump is now making a strange noise. What is this noise? Thank You.