I read once that the injectors will tick at low engine speed under some conditions due to them having to close under a greater pressure because at low speed they are not open as long. At faster speeds the tick would go away. A lifter ticking would just get to be faster ticking at higher speeds. Again, I'm not a mechanic that's just what I read somewhere. After my 5000 mile trip this summer to Calif. by way of CAA my car ticked alot at low speeds and idle but went away if it was reved up. It did that for a couple of weeks and now it doesn't do it so much.