Call of Duty 4 - Time Trial Video

Found this youtube yesterday. Apparently if you use the pistol, sprint through the whole course and shoot the targets through the walls you can get times under 15 seconds. It's hard to tell if this is a glitch or not because you are told that your shots can go through some objects like plywood and you're not forced to use the MP5 (you're only reminded to equip it before the start).

See for yourself. Personally I don't think it's glitchy, just clever.