problem with sound alerts on iOS 6

Hi all,

Since I upated to the iOS 6 on my iPhone 4I get no sounds with most of my notifications (incoming email, calendar alerts, text messages etc)

Sometimes it works but very intermittently. Sometimes it's the wrong sound as well.

I get the pop up notification (which lingers on the screen) but no accompanying sounds.

Do not disturb is off and the volume is at maximum.

I've already done a reset (erased everything and started from scratch) after the installation of the iOS 6 as a lot of things went wrong.

help! 🙂

thanks