Okay, I think you can rule out the tilt switch. It may still be the alarm, but this is looking less likely.
Looking at the wiring diagram, there are two components that are closely linked to the hazard lights and the indicators. These are the flasher unit (which has separate inputs for the turn signals and hazards) and the crash control module (which amongst other things turns on the hazards in the event of a crash - the alarm also seems to feed into this). The only other thing I can think of is the indicator switch on the steering column. Of those, the easiest thing to swap is the flasher unit, but they are not cheap, as they are somewhat more complicated than a simple relay. If it is not the flasher unit, then I am thinking that something is causing an intermittent short to ground - either in the indicator circuit or in the crash control module circuit and all the stuff that plugs into it.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc