steam return line

HAPLUMBER

I JUST GOT BACK FROM A JOB WHERE THE PEOPLE GOT THIS HOUSE FROM AN ESTATE AND TO MAKE A LONG STORY SHORT .......... THEY ARE GETTING SURGING AND BANGING @THE END OF THE STEAM MAIN AND THE RETURN LINE IS HOT FROM THE END OF THE STEAM MAIN TO THE BOILER THE RETURN LINE IS 2 INCH AND THE BOILER IS CLEAN THE WATER IS IS CRYSTAL CLEAR ...I TOOK OUT THE NIPPLES AT THE BOTTOM AND THE TOP OF THE BOILER AND THERE IS NO SCALE OR DIRT IN THE BOILER THE BOILER IS ABOUT 2 YEARS OLD AND THE HOUSE HAS BEEN EMPTY FOR ABOUT 14 MONTHS

ANY IDEAS

THANKS
TIM