I have noticed a possible problem on my car. It also happened on my old car, a Mazda Protege5. On both cars, it didn't seem to happen when it was very new, but now that it's got some mileage on it (I'm at 33000 KM or so), I am noticed a bit of detonation or pinging at first mainly during some shifts. I am lately starting to notice it occuring not only on shifts but also when I start to accelerate for a second, and then I guess the knock sensor adjusts the ignition timing and it goes away. Anyone know what could be causing this? On my Protege5 I figured maybe the injectors were getting dirty so I had the dealership do the recommended injector flush on in, but that didn't fix it. I also put in new plugs and that didn't change it either, neither did a K&N air filter. It is only for a split second, not persistant or anything but more and more frequent.
Why is this happening, is it normal, will it cause damage, and is there anything I can do about it?