i'm going back to your first post. have you done anymore work on pinpointing where that noise is coming from. is it still from the front?
many mechanics (and customers too) can attest to any number of weird coinsidences. if the knock *is* from the front, then it has nothing to do with the oil change, the oil filter or the phase of the moon either.
and you are right back at the initial ideas of the timing belt tensioner. it is common for the knock to go away at higher rpms of ~2500 rpm. it's one of the ways you can discount it as a rod knock.
many mechanics of nonisuzu persuasion are not aware of this phenomonen. they attribute the noise to lots of things and even want to rebuild your engine. while you have a NON-interference engine (meaning you won't get valve and cylinder damage if your timing belt breaks) there are advantages to doing it before the belt tears up the timing belt covers, for example. you will do at the same time: timingbelt, timing belt tensioner and water pump. possibly also cam seals, and timing belt tensioner pulley if indicated upon inspection.
if you look up top in the FAQ there is the idea it could be something with the serpentine belt hardware (though i haven't heard that before for this kind of knock).
any new info ?
\\bc