Uk Turbo advice

New to the forum and new to impreza's so not sure if this is posted in the correct section.
Basically I've just bought a 98 UK impreza Turbo (WR Prodrive). I'm over the moon with the car, it's very clean and drives like a new one. It has 110K on but has full service history and has always been well looked after (folder full of receipts going back years). The only issue with the car is that on these cold mornings upon startup the engine sounds quite tappety. Once the engine gets up to temperature the sound totally disappears. I've checked the oil and found it is on the correct level and seems nice and clean. I am goin to change the oil and filter anyway to millers 10w60 for peace of mind. Just wondering if anyone has come across this problem before? The noise is definitely a top end noise. The car is otherwise perfectly healthy. No smoke, knocks or bangs, Boosts at 12 PSI, stays at a nice temperature etc.

I used to get piston slap on the first Impreza that I owned, it made a right racket when I fired it up on a cold morninb but seemed to calm down after it had been running for a while. I think a lot of the older imprezas do this from what I've heard.

Every impreza I've had has done this

Cant beat a bit of a rattle.
keep it regularly serviced .
let it warm up and cool down before and after spirited driving

Seems like you've bought a normal Classic, enjoy it.

 Mine done this from day 1 i had it, WAS going strong until the wall jumped out at me,