When I accelerate at about 2500rpm I hear a "clattering" or "rattling" sound. I assume it is detonation. I was advised to try a higher octane fuel, which I did. I also used a fuel additive (octane booster) which has not had any noticeable effect. I have read that a "colder" plug may fix the problem. So what exactly is a colder plug and could it have any adverse effects on my car? If this is the route I should take then what plug should I try. Are there any other possible causes and cures for this problem if the plugs don't work?