It sounds like an exhaust leak, but I have had two different exhaust places look for the sound and they couldn't find it. Although, I don't think either of them checked the egr tubes in the back of the heads, I don't think they could make this ticking and I checked and they seem to be tight. The ticking gets louder the warmer it gets, because when I first start it I can't hear it at all, even when I am next to a curb. After it warms up, it is plane as day whether I am next to a curb or not. I am thinking maybe roller rockers, but don't understand why it would only be when they are warm. I also considered pinging, but my timing is set at 16, which isn't high for aluminum heads, and I run 93 octane. The sound seems to be coming from the back of the engine, but it is hard to tell. Oh yeah, and it really is only noticeable from about 2000 - 2500 rpms. I am at a loss, if anyone can help me pinpoint this I will mail you a 12 pack of your favorite beverage. Seriously though, I will!!