2015 RAM 1500 Black Sport. Mine did this the other night on its own when the truck was in the garage and had been turned off for at least an hour. The alarm/panic went off all by itself, the key FOB was not in my pocket, it was on the kitchen counter so there was no triggering of the panic button. I started the truck, backed it out of the garage, turned it off, popped the hood and began to disconnect the battery and the alarm/panic honking went off after about 1 x 1/4 turn of the nut on the black battery connect. I tightened the cable back down, closed hood, and drove it back in the garage. The honking would not stop by hitting the lock, unlock, or panic buttons on the key fob. This is the first time this has ever happened to me.
I recently had the hood replaced by Chrysler, and installed a Corsa muffler back exhaust system on my own last weekend. Maybe some loose trons? I re-connected the stock muffler grounding cable when installing the Corsa muffler.
Just weird this happened.