Some SMS from companies have text instead of number in the from field. I noticed that no matter what I choose in notification settings I still get the default loud notification on these messages. For example, my bank sends messages from "Tinkoff" number and I can't silence them. I tried to add this number to contacts (it's displayed as 8465633) but it didn't help. Regular numbers can be silence or customized and I have no issues with them. Only with these custom text numbers that can only be used on SMS gateways and such (not for regular users). I also disabled the default messaging app completely (in system settings) so it's not that app making sounds.