[Q] In desperate need of help / advice - sony xperia z2 constantly switching off topic

Hi guys I am a new member here, so basically my problem involves; my Sony Xperia Z2 keeps turning off whenever I play something on full volume; outloud. I own a refurbished device as my new device broke due to water damage, I sent it to my insurers (TSB) and at a charge of £50, they sent me this. Bare in mind I have had this phone for little less than 4 days, it is also hassle to send the phone back again and claim again, so i was just wondering if there is any software related problems which I could fix - I read something about uninstalling google now, but I have no clue how to uninstall this.

Thanks for your help in advance.