Why my Galaxy Note 4 is overheating when I don't use it?

[AC Question]

I have Galaxy Note 4. It was working fine but it used to heat a bit. When I upgraded to Marshmallow the situation got worse. While using internet or playing games the device heated up and I was unable to hold it, even the earpiece got very hot. Last week water got into the charging port of my note 4 . I blew it out and kept it for day or so. Then after putting the battery inside it, the device worked. But now when I power on the device it starts to heat up. I don't understand why it is happening on normal use. Please help . everything else is working fine but the device gets hotter even when i'm not using it. Is the battery affected? or the water had damaged something in the device?