Don't know whether you already have a solution for your WRX tick, but found this on the web:
3 Causes Of Engine Ticking Sounds Coming From Subaru Vehicles
17 August 2015
Categories: , Blog
Subaru utilizes the boxer engine in their full lineup of vehicles. The boxer engine features horizontally aligned pistons, which puts all of the connected components at an interesting angle as well. This angle may cause excess stress on the components over the life the engine. To keep your Subaru in great shape, it is important to maintain a strict maintenance schedule to halt developing problems before the issue escalates. One of the most common signs of a developing issue is an acute ticking noise coming from the engine compartment. If you hear this ticking sound from your Subaru, it may be one of the three following issues.
The valves in the head of your engine sit nearly sideways to line up with the rest of the internals. As a result, the clearance spacing between the rocker arm and valve surface can have quite an impact on the valves' performance and noise levels. If your valves start making a ticking noise, you must have them tightened down to the appropriate specifications for your engine. Technicians use a feeler gauge and torque wrench to make those precise adjustments.
The fuel injectors operate using extremely high pressure ratings to create the appropriate spray pattern. When placed at an angle for the boxer configuration, injectors have to work extra hard to send fuel jetting into the engine at the proper rate. This extra effort can result in rapid wear of the injectors' moving parts. When the injector starts to wear down, it will develop a constant ticking noise. If this problem goes on too long, the injector will eventually fail and cause lean conditions, which could overheat and damage your engine internals.
Due to the unique layout of the boxer engine, the exhaust pipes coming off the manifold are exposed to excessive temperatures. These temperatures can break down the metal materials quickly, resulting in an exhaust leak. The exhaust coming out of the resulting holes often makes a rhythmic ticking noise. When this problem starts to develop, you might even notice a slight smell of exhaust in the cabin area. In addition to making a racket and smelling bad, the leaking exhaust could also cover the engine bay in a thick layer of dirty soot.
Sourcing The Issue
Your technician will usually use a stethoscope to pinpoint the location of the ticking noise. Reviewing your vehicle's maintenance records and performing a visual inspection can also help identify the direct cause of the ticking noises you hear. Upon making a positive diagnosis, your technician should present you with a work order detailing the services required to halt the ticking and return your vehicle to an optimal running condition.
In any case,
May the WRX be with you