Share your experience!
Hi James,first,music stop for 2 second while swap application?Can you elaborate more a bout it?
Second,When a notification arrived,the music will automatically stop for a while,thus noticing you that there is notification.But this only happens if you assign a tone for it.Or you did assigned a tone but turned the "Ringtone&Notification" volume to silent.
Yes,you can disable this from happening,follow these steps:
1)Go to Settings->Sound->Default Notification->Flick upwards and choose "None"
2)Press back,and tick "Vibrate when ringing".
So this will vibrate only when you received a notification.Hope it helps! 
Thats probably lag.Maybe too much opening at the same time.Or the phone is just overheating.