I've only had the phone a few weeks and it's always done it, though not to this extent. I also have audio dropouts on my Bluetooth earphones when watching videos - the sound will play for around 5 seconds, then mute for exactly 30 seconds before returning. I do wonder if I have a faulty handset?
Please try this. Go to settings, accessibility, advanced settings, notification reminers (you may see the link in the "looking for something else?" box and turn this off. If you can cross your fingers at the same time, that may help.
Report it to samsing. If it has started since you got the phone then it might be their fault. Not sure though. If I was you I would report it to them and say it has been doing this since you got the phone a few weeks ago