DIAGNOSIS Some heat is normal—that's the side where the main internal amplifiers and power supply components are located. They generate heat when driving all those speakers, especially at high volume or with heavy bass.
FIX First, ensure it has proper ventilation. You need at least 4 inches of clear space above the soundbar and a couple inches on all sides, especially that top right side. If it's tucked into a tight media cabinet shelf, the heat has nowhere to go. Move it to a more open spot if you can. Second, check what sound mode you're using. Modes like 'Cinema' or 'Music' that push the sound harder will generate more heat than the 'Standard' or 'Auto Sound' mode.
IF THAT DIDN'T WORK If the heat feels excessive (too hot to keep your hand on) or you notice the sound cutting out or distorting when it gets hot, it might be a sign of a failing component. In that case, the only fix is to contact Sony support. Note when it happens—is it only after 30+ minutes of loud movie watching, or does it get hot even at low volume shortly after turning on?
HEADS UP Never put anything on top of the soundbar, like a game console, streaming box, or decorations. That traps the heat directly against the electronics and can significantly shorten its lifespan. Heat is the enemy of amplifiers.