I had a tick on my truck at one time. Crawl underneath the truck and have someone tap the starter to slowly turn the crank. Keep an eye between the harmonic balancer and the timing cover. If the balancer is 25 years old the rubber will start to protrude from the back and slap the timing cover on every rotation. If that's not the culprit then its probably the ps pump. Replacing my balancer made a big difference on mine. When I replaced my pump a new tick emerged. Doesn't really bother me and its slowly getting quieter.