Hazards flashing rapidly on start or stop

When I switch off the engine on ou euro5 2015 build Fairford sometimes the hazards flash externally rapidly for a about 5 seconds the dash light doesn't illuminate but I can hear a relay clicking behind drivers side dash. It's also done this on start up, van fitted with an aftermarket tracked immobiliser. Has anyone else experienced this?
Thanks in advance

Ive spoken to the security system manufacturer and monitoring centre who seem to think this is related to the alarm. Ive been reassured it's working correctly as they can perform tests remotely but want to have a look at the vehicle when it's convenient to me, unless it becomes a problem in which case they will send someone out. In the short time I've had the vehicle I've triggered the alarm a number of times and received a phone call on each occasion within a few seconds of the activation. I have been impressed by the service I've received from them.