My 22RE('91,R Cab) knocked big time w/ 87 octane, minimally w/ '91 octane, then the long block was replaced w/ rebuilt at 160K miles, using all the old engine control/fuel systems, etc. Spark knock IDENTICAL as before, thereby proving that, in this case, it had nothing to do w/ "carbon buildup" in the cylinders. I like the "crud in the EGR tube" idea...
Incidentally, when I drive around at higher altitudes not in CA(Utah,etc) the knock goes away. Just repoting the facts over here.