2018 GMC 2500 work van randomly tries to start itself

A dear friend of mine drives this van. It’s his work vehicle. It has 37K miles on it. Just today as he went to start the engine and leave, I could hear his starter solenoid engaging repeatedly about every 1/2 second. Then the engine started slowly cranking over. He pulled the keys back out and showed me and it was still doing it. Apparently this is a regular thing. If it sits for a few days, he gets in, turns the ignition on and it just does this. As soon as he turns the ignition to the “ON” position, not even trying to crank it. The solenoid starts clacking regularly as described and after a few seconds it’ll try and crank the engine. Afterwards, the battery goes dead and he has to hook his jump pack to it. Maybe the battery is pooched so that might be unrelated but I’m wondering since he got it used, could there be a remote starter in there and it’s messing up? That’s all I’ve got. If there’s something else that goes wacko I’d have no idea. If there is a remote starter, how could I tell? I don’t know if his key fob has buttons for it and as far as he knows, there is no remote starter hooked up to it.