Elantra HD (2006-10) :: Goes Through Two 20 Second Honking Cycles

Our 2007 Elantra horn keeps honking for about 20 seconds in the middle of the night, for the past week. Every night at about 1245 am it goes through two 20 second honking cycles with about a 10 second gap between the two cycles. The again at 230am, then randomly every hour until 7am.

We lost one of the fobs recently and the other was destroyed by a lawnmower a couple years ago. We figured someone found our fob and was pressing the panic button at night, but who would do that on a schedule? We had the dealership disable the cars receiver, it still honks.

Went back to dealership and explained that we found a bunch of similar stories which pointed to the hood switch malfunctioning. They said that was most likely not the case. They also said they didn't think they could fix it if they couldn't replicate it. They disabled the hood switch as a precaution, still honks on schedule.

For now I am disconnecting the battery at night and tomorrow when I find out where the horn is located, will disable it. I know that's a safety violation though. What other choice do I have. I have two theories.

I disconnected the battery to reset the car's clock. I figured if it was honking on some schedule, with the clock reset it should have changed, but it didn't. I suppose there's another CMOS type battery in the system keeping the odometer and other electronic data alive, which could also be holding this schedule.

My other theory is there some sensor malfunctioning at night as the temperature drops. Hard for me to prove or disprove this one.