yup...the sound will get louder when the engine is hotter... it's normal...
does it sound like this ?
YouTube - Blacktop 4age 20v
YES, EXACTLY!!!! But the one in this video is quite serious. Mine is slightly better than this one. Damn, I hate that sound... It's like you lose faith in the engine and never know when it's going to break down on you.
Talking about RON95, I just finished a full tank of Primax 95 Xtra and compared it with Shell RON95. I would say mileage wise, both almost the same. Similar driving habits, Primax 95 Xtra was at 515km, while Shell can give me 520km. That means old Petronas fuel technology is worse?
As for the 'Umph', I feel Petronas fuel lack the 'G' feeling when accelerate. Somehow the Shell RON95 combustion is a lot stronger, maybe due to the additives in it. One thing I feel is that engine sound is quieter when using Petronas 95 Xtra. Shell RON95 gives you a harsh feeling, but more power.
Engine knocking wise, both feels the same, so i believe fuel is not a factor to the engine knocking, but the VVT pulley is as advised by chinozie. Now one interesting ques, can be sound be eliminated by fixing the oil control valve (OCV)? I've seen some forum discussions trying to drive with their engine with the OCV unplugged, purpose is to disengage the VVT. Will that actually harm the engine itself?
So my conclusion, if you want power, with good mileage between the two choice, I'd say Shell is the winner.