Radiator Heating System, 1920's home with updated piping. Extremely loud banging ONLY when heat comes up. We've isolated the noise to just one side of the house - loud through 3 floors though. Understand it may be a pipe pitch issue, but don't know how to investigate. Had one plumber in who told us it's basically hopeless which is unacceptable of course.
I've had rattling in radiators in other houses, easily fixed by bleeding, but this is NOT that. This is over-the-top loud banging in pipes.
Thanks for any advice.

The loud banging is hot steam coming in contact with cold water sitting in the pipes you must get more pitch back to the boiler there is no other way around it . Mikie D

Get rid of that plumber, it's he that is hopeless. Make a few calls to reliable heating contractors... explain the problem and see if they would be willing to come out and give you an estimate to stop the problem. Talent and experience win out over "hopeless" every time.