I did replace the alarm module which I located under the cowling as I previously mentioned with a new module.. That module contains the actual siren, and self contained battery.. That battery is needed I. Order for the siren to sound even if the battery terminals are disconnected from the battery.. Added security I guess.. Sometimes over time the battery leaks and corrodes the circuitry making the alarm do funky things. In my case the chargeable battery inside the module was completey dead and hence my alarm wouldn't even sound.. Only the lights would flash.. After putting a new module the siren would also sound... My issue was Bcm related and I couldn't unlock my car with the key fob, and when I would unlock it using the key it wouldn't disarm the alarm and hence the alarm would sound and I couldn't turn it off.. Eventually it would just stop on its own..
I'm not sure what your situation is with your alarm... If it isn't lock related like mine was and just going off on its own.. It may be alarm module issues and replacing it may resolve it.... But who really knows unless you actually do so..
I'm not sure what you are talking about a switch under the hood..l there is a switch in the cabin related to the tow away alarm disarm etc... On the center dash.. Don't think that it would have anything to do with your problem though..