Intermittent ticking noise in 2015 Subaru WRX

Question

I've been hearing an intermittent ticking noise in my 2015 Subaru WRX that I can't seem to pinpoint.

The car is bone stock with ~45k miles on it and is still under warranty, but I'd rather not spend half a day waiting around without my car only to get a "could not reproduce" from the dealership.

Description of Noise

• The noise has gotten worse since I started hearing it, and now that I can hear it better, it appears to correspond (at least somewhat) with engine speed.
• I'd estimate the frequency to vary from around 2-6Hz.
• It sounds like it is coming from the engine compartment.

When It Occurs

• It only manifests itself during/shortly after the engine has been under more than a slight load (enough load that the turbo is creating positive pressure in the intake i.e. >0lb of boost).
• I can hear it when cruising/accelerating around 2K-4K RPM.
  • It is drowned out by engine and exhaust noise above that point.
• I can hear it for the following 60sec or so of decelerating or coasting.
• I can't hear it at idle but can occasionally hear it when the car is parked and revved up then allowed to spin down (i.e.: accelerator flat on the floor from idle to 4k RPM, then fully released).

The noise is not there every drive:

1. I initially heard it Monday.
2. I didn't hear it all yesterday.
3. I heard it this morning on my way to work (after about 45 minutes of highway driving).
   • Once it started making the noise, it didn't stop until I parked (about 10 minutes of city driving).

Diagnostics

• It immediately vanishes when disengaging the clutch (pushing down on the clutch pedal), but returns when the clutch is re-engaged.
• Engine temperature doesn't seem to matter, it made the noise immediately after starting.

Questions

1. What could be causing this?
2. How do I further diagnose this?

Resolution

Took it to the dealer on 28 Nov, they looked at it and are replacing the clutch and throwout bearing.

Answer 1

Given that the issue vanishes "immediately" upon pressing the clutch, I would guess that the problem lies somewhere in the transmission or its linkages. The already mentioned throwout bearing is a possibility, especially with Subarus. Given everything you wrote here, and the well known throwout bearing issue, that seems the most likely candidate. Here is a link to a WRX forum where a bunch of people have failed throwout bearings: http://www.clubwrx.net/forums/transmission-awd/134420441-2015-wrx-throw-out-bearing.html

If it isn't the throwout bearing, it could be one of the numerous other transmission bearings further down the line. I wouldn't know where to begin chasing down a failed bearing inside a transmission, and since its under warranty, you shouldn't have to.

Since the ticking is independent of engine or wheel speed, you are probably safe in assuming it isn't one of the other bearings elsewhere on the vehicle (wheel bearing, diff bearing, pulley bearings, etc.) You would expect those to modulate directly with engine and/or wheel speed.

Answer 2

Hm, I am thrown off by your mention of the clutch, throw-out bearing and deceleration notes, but I figure this is worth mentioning as it otherwise fits the bill.

There is a TSB/recall for 2015 Subarus with the 2.0L FA engine for pre-ignition causing the noise you otherwise seem to be experiencing.

Subaru Service Program WQW-5

Subaru has developed a modification to the Engine Control Module (ECM) software logic due to a possible pre-ignition issue on certain 2015 model year WRX vehicles and certain 2014 and 2015 model year 2.0XT Forester vehicles, equipped with a 2.0 liter turbocharged engine.

Under certain high engine load driving conditions, engine combustion may occur prior to spark ignition resulting in elevated cylinder temperatures and pressures. This could cause a rough idle and engine noise, and if left unaddressed it could lead to excessive erosion of the spark plugs and possible engine damage.

You should be able to get this checked against your VIN to see if you are affected and fixed at any Subaru dealer for free.

Answer 3

It immediately vanishes when disengaging the clutch (pushing down on the clutch pedal), but returns when the clutch is re-engaged.

Clutch release bearing or pressure disk, or both are gone. Shouldn't since it is a relative new car, but sounds to me that if you hear a ticking when clutching, the pressure disk has an uneven pressure finger off, and possibly damaged the bearing...