Detonation is spark knock or 'fuel knock', also typically called 'ping.' It is a light, irregular 'rattley' sound caused by low-octane fuel or by spark timing that is too far advanced. It shows up mostly during acceleration. From your description, I think you can discount that possibility for now. Although the possibility is not out of the question.
Since the knock in question seems more noticeable with the warm engine, I would suspect a valve lifter, or some other oil-related condition. What happens if you shift to neutral and let the engine idle when you hear the noise while on the road? Noise disappears, continues? If it disappears with the transmission in neutral, can you bring it back by changing engine speed- transmission still in neutral?
At this point, I don't think you have a piston or connecting rod matter. A connecting rod remains a possibility, but you should be able to hear that if you speed up the engine gently to a couple thousand RPM and release the throttle slightly. In the very early stage of rod bearing wear, a knock tends to show up just as the load decreases as you release the throttle.
Hope this helps. Keep in touch. I'm sure others here will have more ideas as well.
Harvester
