Galaxy S2 a bit quirky

[MSCOFF]

My S2 about 14 months old (StraightTalk SGH-S959G) is behaving oddly at times. Not any one particular app. Pandora came on yesterday all bt itsself. Sonetimes the disolay needs to be reset to landscape mode. Or flight mode comes on all by itsself. Other apps sometimes startup . Phone works fine. Calls in/out ok. WiFi ok. Turns on/off ok. But it acts occasionally like a pet that goes its own way. Not a big enough problem to consider a new phone. But is there ant fix aside from trying a factory reset and start all over. Phone is stock with no mods, unrooted ect. The behavior seems to be systemic rather than limited to ne or two apps. Thanks for any suggestions. Mark S