Since upgrading iPhone 4 to ios 7 I have lost sounds on emails, calls

Has anyone had this problem. It did used to happen occasionally before, but since upgrading to ios 7 I very rarely get the ding for email etc when received or any sound when someone calls me etc. I ahve checked the button on the side, volume and the settings and all are ok. I test it by getting someone to text me and it sometimes works and sometimes doesn't.

is there a fix for this yet????