I've now got an ultrex dump pipe installed, and have had the car tuned to suit. Very different car now to standard and is great fun to drive.
I have just noticed a knocking / tapping sound over 3k RPM, most noticeable from 4k onwards. Quite noticeable when raising revs slowly with window down while moving, can't hear it with windows up. Sound is there when revving in neutral but much less. Seems to only be present under throttle, during deceleration the sound disappears.
The sound reminds me of when I spun the big end bearing in an old N/A car I had years ago... but much less noticeable / severe. I'd say it's mild sounding right now. 'll try to get a video of it. The sound follows the RPMs from 3k onwards but can't hear it once revs get say past 5.5k RPM (probably because so much noise). No difference in power at all (from seat of pants feel anyway).
I am thinking it could be rod or big end bearings. Any way to identify this via RomRaider logs? They're all clear so it's not pinging (no FKC / FBKC showing up, IAM still at 1). I'll drop the oil out this weekend and see if there's metal shavings present.
Hoping it's not time for a new motor
Update: further research leads me to think it could potentially be the timing belt tensioner. I’ll have a look into that and report back!