My phone keeps going silent when I put it on charge... Not every time but most times I've checked all settings

When I put my phone on charge it will automatically go to silent ( ringtones, texts, mail, music, videos) I've been through all settings and I fiddle with the sound buttons on left hand side ... I've cleaned the phone in the correct manor to make sure there isn't anything inside the sockets or headphone socket ... Also I use only origins iphone charger no docking stations nothing else gets plugged into my phone any help?