Why is iPhone 4 heating up after screen replacement?

I replace iPhone 4G LCD Touch Digitizer Screen and also the phone had some water damage. I took it apart and place all parts in tupperware with rice for 48 hours. After assembling it together it turn on and all functions work but from camera and my concern is the top right side of the phone is heating up a lot it is around the power button and back camera i have no idea where is it coming from. I try to replace the batter and still the same. I also look check the lower antenna connector to make sure is connected right. Any advice?

Thanks!