Strange grind type noise

Hi all, got my mk1 octavia vrs project on the go and started to make progress. Passed its MOT the other day with only a couple of advisories (they advised my lowering springs and that I'd sanded down and painted my subframe, would you believe). Ever since I bought it, I've had this strange noise from cold starts though. I start the car and drive it ten yards to my front door, then leave it idling, and a couple of seconds later there's this strange grinding noise, that vanishes after a second. Turn the car off and restart it and it doesn't do it. 

I often feel like the power is a bit lower sometimes too, but it's possibly just my imagination. 

Worst nightmare is if it's the cam chain, best case scenario is it just needs a better grade of oil. 

Have changed the oil pick up, which was blocked and was done 5k miles ago, which makes me think it's maybe starved the tensioner and stretched the chain, and serviced it at the same time with 5w30 dealer oil. SAI has been deleted as has the charcoal canister. 

No noise when driving, and no fault codes.