Check your phones settings see if there is something missing in one of them or maybe firmware for phone needs an update.?

I'm not getting an alert sound while listening to music through normal headphones. There is no notification sound when the phone rings, text is received...etc. The volume of the music does go down a bit for a brief period.

Phone: Nexus 4 with Andriod 4.3
Headphones: Bose QC3, 1/8"
MMA: Version 1.0.4.0156