Look to where the white wires are joined and all come back to the electrical box. Very often you will find that the connection fairly close to the main box gets hot because of loose connections.
A very useful tool in this situation is a laser thermometer probe. You point the laser beam at the hot spots and it gives you a readout on the back of the pistol device of the temperature. I got mine on sale for only $30 and have used it to detect cold air coming into my house, tire temperatures while running the rig, and electrical box hot spots as well. Just point and shoot.