You probably have a “one pipe” steam system, which uses an oversized pipe to direct steam to the radiators and also to collect condensed water to return to the boiler. When these systems are not properly designed, return water blocks the pipe and this lead to a lot of banging noise as incoming steam meets the condensed return water. Sometimes after many years scale or sediment builds up in the pipes and radiators. Even well designed one pipe systems “bang” somewhat. If it’s excessive you may have a poorly designed or partially clogged system
So: flush and bleed the radiators and consider flushing the boiler and pipes as well. You should have a licensed plumber do that job, because steam boilers are potentially dangerous.
BTW, you can tell if you have a “one pipe” system because there is only one pipe coming into the radiator which has an air vent. Two pipe systems have an inlet to the radiator (with a shut off valve) and a return pipe (with a steam trap to prevent steam from entering the return pipe). If the traps leak, you will waste steam.
Anchoring all pipes is of course essential in all plumbing, but in the case of banging steam pipes, it doesn’t help much because the pounding force of the steam against the pipe obstruction is so great.
NtP