Rattling and knocking since changing spark plugs?

Six weeks ago I replaced my spark plugs with Denso IXEH20TT. I didn't have any issues before, but the car has done 205,000km (130k miles) so it's due and I doubt they've ever been changed before (at least they haven't for 6 years I've have it).

Since I changed them I've noticed a slight rattling noise when the engine is under medium load. It's not noticable in the car, but is when the windows are open. I thought at first maybe it was the exahust is going (never changed, 12 year old car) so didn't think anything of it, other than it being a coincidence. By medium load I mean the power guage is towards the end of the 2nd section. Under high or low load (engine idling) it's doesn't happen.

For the last two weeks I've been on holiday and the car was parked at airport parking outside. Yesterday when I first started the car I had knocking for 15 seconds. It's was 8c outside, so not really cold (our winters get to -25c and never had issues starting before). I drove home and didn't have it again throughout the journey. This morning again no issues, however we have underground parking which rarely gets below 18c. 12v battery was replaced a couple of years ago, and hybrid battery was showing 6/8 bars.

I've also been noticing the oil smells like petrol for the last couple of months. As I understand this is the PCV, which I intented to replace with the spark plugs but it didn't arrive in time. I am not loosing oil or coolant, and all fluids (including transaxle) were replaced last year.

This weekend I plan to replace the PCV and take a look at the EGR and throttle body (never been cleaned). Once that's done I'll replace the oil as it's nearly due. Anything else I should look at while I'm there?