When you are in the Phone App and you use the dial pad to dial, it will create a sound. But if you use your speed dial or dial from your contacts, there is no sound. You can mute the sound from the home screen(swipe down, click on the bell icon that has notifications, it turns blue when it is muted), or use your volume up and down keys for the sound.
The slow down is not normal for your blackberry, I actually find it the smooth and super fast phone. When I compare it to my wifes Iphone 5, hers is very slow compared to the z10. Try a battery pull and re-boot your phone, just to flush out any app that is slowing it down.
