You said the sound is comming from the right side of the engine compartment. Is that right side when facing the open hood, or when sitting in the drivers seat (passenger side or driver side)?

If the problem goes away when warm, I can only assuem that it's the valves and it may be normal. The colder it is, the more clearance there will be in the valves. Because of this, the clearance must be checked when warm.

The other possibility is that the cam chain (timing chain) tensioner is not working properly. I beleive this also utilizes oil pressure to tension the chain.

As mentioned before, this could be partially related to oil viscocity. This car recommends 5W20. If 10W30 or 10W40 were used, you might have excessive valve clatter when cold.

I doubt the noise is actual engine knocking. When cold, the mixture is set rich by the computer. Rich mixtures slow fuel combustion and are therefore less likely to cause knocking.