Intermittant knocking noise from engine

[yods]

I will chuck up a video but here are the cliff notes

- Noticed engine noise change slightly mid-way through a track session. No loss of power, not significant. Tappety noise (not thunky like big end) occurs a few seconds (at most) after startup very briefly.
- Noise also prominent during mild throttle changes between 2500-3500 rpm (approx). Large increases in throttle do not seem to produce the same results.
- Car was retired, oil dumped (oil was lower than ideal for a track day ) but no metal or shavings. Filter hasn't been done yet however.
- Car is NB8BA with VVT. The lack of consistency in when the noise occurs makes me think this somehow related.
- Car drove 700kms home without issue (apart from a slightly stressed driver) - babied most of the way, although it should be noted that freeway speeds are in the troublesome range is 6th.

Apart from the stethescope/screwdriver method of pinpointing the noise + a compression test (Not sure what this will show), is there anything else I can/should look at before taking the motor out? Is it worth removing the valve cover for example?

First remotely serious issue with a non-subaru so don't have a good troubleshooting process yet (thankfully!)

Cheers
Peter

[greenMachine]

Someone else has just lost an engine at a track day, probably due to low oil level, or low oil level being a significant contributor - that was definitely bearings.

But before doing something drastic, take the oil filter apart. I am pretty sure the oil enters the outer part, so you need to cut it open to inspect it, but if there is something there you would probably have seen it in the bottom of the pan you drained the oil into. If there was nothing there, and nothing in the filter, I would look elsewhere. I haven't got VVT, so can't comment on that as a possibility.

How low was the oil level, and if you have you refilled the sump to full does the noise persist (presume you topped it up for the drive home)?