What u/JoBo said.

I’d look at your wiring. My first thought is there is a short being crated as you walk over that area. It is pressing the wires together

And to be honest I really can’t think of anything else.

Yes I’d look at the floor in the loft. I’d also guess that’s easier than taking apart the ceiling.

I’d also poke in and around the wiring harness for the alarm