Another tapping question

[sparks12kv]

I've been checking the existing threads about tapping noises, specifically coming from the engine. Nothing matched my symptoms, so I thought I'd post here. If this has been covered already, feel free to delete.

 

My new-to-me 07 Leg NA 5mt has a moderately loud tapping only from 3k to 4k. Between those rpm's it taps loudest under partial throttle. It's gone when I'm fully off the throttle, and either the tapping is gone or drowned out when my foot is buried. It taps under all conditions, when cold or hot, whether first starting or after a 5 hour drive. It also stays tapping if I go into neutral while maintaining rpms, and it does it in all gears.

 

After reading lots of other tapping threads, I took it to a competent muffler shop and they found one rattling heat shield on the header by the outlet flange. They hose clamped it, but the sound stayed the same.

 

I also did an oil change with Rotella T6 to see if it would change the tone, no change in sound.

 

It does potentially have a failing cat. Previous owner had code 0420, but I reset the ECU and it hasn't come back, after a 300 mile trip. It's definitely not down on power, doesn't have any flat spots on power, and it's as quick as any other 2.5 VVT (so, not very), it's just tapping. Anyone heard of this before?

[apexi]

p0420 could be a bad rear oxygen sensor. If the rear oxygen sensor goes bad, it can't correctly monitor the cat, and it'll falsely throw a p0420.

 

Or the sensor could be good, and your cat really could be bad.

 

Subaru's make some funny noises. I wouldn't be too worried about a tapping noise, a knocking sound would concern me though. Tapping noises seem to get worse in the winter time and when the engine is cold, I think piston slap is the cause in cold weather.

 

It can be hard to capture audio of engine sounds, but I'd give it a try.

[sparks12kv]

Yeah it's not the first time I've heard Subies make noise. But this is the same cold or hot, starting or after a long drive. Always the same.

 

Anyone seen a failed cat make a rattle internally like this?

[kzr750r1]

The cat element can degrade and begin to bounce around inside the cavity. I've ejected the remaining element out of a truck before. Only way to really tell is drop the down pipe and take a look for yourself.

[sparks12kv]

I've been hoping that was a possibility, so that will be my first course of action.

Really I'm just looking to make sure it can't be valves because it only taps at specific rpm's. That way I can go ahead with a timing belt job. It's either fix this motor, or jump ship to build a new one.

[kzr750r1]

Yeah I have a noise that has come up under toque requests and I"m starting to lean toward drive train but could still be motor as well... Until found it's a riddle wrapped in an enigma. Good thing I just picked up a backup ride. I have a feeling I'm going to be tearing into my car again soon.