I have had a very similar problem, I drive a '97 R33 GTS25t pod/3inch turbo back zorst.
The problem occurred the day after I installed an Apexi SAFC2. After sitting on 90kpph for 5mins I started hearing clicking noises near the passenger seatbelt and then the HICAS lights came on. Car still drove normal, I stopped on the side of the road and the ticking noise continued and HICAS were still lit. Turned the car off waited 30sec and turned it back on the HICAS lights were off but the ticking noise still comes on intermittently (usually at high speeds).
Since then there's an occasional ticking noise near the floor of the passenger's seatbelt but the HICAS light have not lit up since and it has been about 2weeks since the first incident.
If anyone has any ideas please shed some light on us.