Engine knocking in high RPM range

Hi, one of the Subarus I’m tuning having a weird knock events happening at the same rpm range starts at 6800 rpm onwards. The car running on 98 RON fuel and I’m sure it has nothing to do with timing because I reduced 4 degrees of timing to a point where the car started to hesitate and it dropped horse power dramatically but the knock events still happens at the same rpm range. Another weird thing is the ecu is not detecting knock so no knock retard how ever I can clearly hear it over the knock monitor. At the beginning of the wot run I can hear normal engine noise until around 6800 rpms where I can hear the knock and lift immediately. The AFR on target (10.5). Anyone has an idea on what’s going on. I’m thinking maybe the spark plugs? (NGK iridium heat range 7)

The first step is quite obvious to me- you should have already tried colder spark plugs with a gap about 0.6 mm and go from there if it doesn't help...

Definitely sounds like knock and not a valvetrain control issue?

It may be simply something vibrating because it's resonant frequency is co-incidentally reached at that point.

If so, you may be able to confirm it by having someone hold the rev's there while listening for any odd noises. Common sources are heat shields and hard lines like for brakes or fuel.

thanks everybody for the suggestions. regarding spark plugs we are waiting for them to arrive and for valve train i will check to see if i can see any abnormalities and regarding vibrations and resonance we did not notice any abnormal noises but we will double check. things i tried so far are:

1. retard ignition timing (-4 degree did not help).

2. added more fuel (did not help).

3. changed CAM timing to reduce overlap (did not help).

i have attached sound clips from the knock monitor for you guys to take a listen. the recording is only form the left channel/speaker just ignore any noise from the right channel.

what do the old spark plugs look like? have you done a proper read on them to make sure what you're hearing is actually knock? if you're hearing it, but there's no peppering on the plugs, it could be (as others have suggested) something else that's ringing at a resonant frequency that your knock monitor is picking up.