I don't know. The article doesn't mention if they are using a city loudspeaker, or their own.
If they want to use a city loudspeaker, they should be shot down. Christians don't get to use city property to exercise their religion, nobody else should either.
If all they want to do is use their own equipment, and this is a noise statute issue, then I'm afraid they have to be allowed. It isn't any different than the bells (well, except for the aesthetic one, which is huge but not contstitutional).
This can be made Constitutional real easy. Just a few more requests to violate the noise ordinance is all it would take. The morons at City Hall would have to start denying requests. Then it would give rise to a Constitutional question.