The thing is, I fail to see how you can. I use those platforms at least four times a week, often more than that, especially the last few weeks. Generally in rush hour, and almost always when the agency staff are on duty. It's implausible that this regular 'shouting' could be taking place and that I wouldn't have heard it.
As I said earlier, firm, raised voices are not shouting and are entirely appropriate to the job of managing a large crowd of people in a hazardous environment. Especially when some of those people seen to find it impossible to obey a simple instruction to, for example, stand behind a line, use all the doors, let people off trains, and stop smoking.
Frankly, I think the restraint and politenes shown by the staff having to deal with the obnoxious ignorance and self-entitlement shown by some of the passengers on those platforms is admirable.