Block echo, as with cross-checking, happens either when Slide Delay stops a block from moving in the middle of sliding while Chip is following it, or when boosting brings Chip closer to the block, to the point of being one square apart. When Chip is sliding in the same direction as a block, he cannot push it according to the Headbanger Rule, and therefore runs into it as if it were a wall, "echoing" back down over the ice. On force floors, block echo has a drastically reduced effect, as on most force floor stretches, Chip can only move backwards one space.
A different type of echo can occur with monsters, such as the echo at the end of Killer Spiral, but this is largely due to the monster order compared to the sliplist, which is the only "order" followed by blocks.
The reason why Chip pushes the block when cross-checking and not when hit by block echo is because the ice corners have special properties in Chip's Challenge: they allow objects to pass over them, but their directional change causes the object to shift polarity before they can pass the ice corner.
Monsters and Chip clearly cannot be pushed, but if a block is pushed before it can move in its new direction, it will respond in the original direction and cause cross-checking. Block echo occurs because a block sliding in a straight line has not changed polarity, and therefore the Headbanger Rule still applies.
Block echo in play
As block echo delays Chip from following a pushed block, it is generally undesirable. Though it usually occurs when Chip first steps on the path of sliding tiles, it can happen significantly down the path, forcing Chip to slide all the way back to the start. One such occurrence is that at square [20, 13] in Block Buster II if Chip leaves out the [1/2] wait before sliding. This wait decreases the block echo significantly, paying itself back in spades.
It follows, therefore, that strategies for reducing or eliminating block echo are similar: wait before following or even before pushing the block, or in more advanced applications, to tinker with the slide delay. Levels where block echo occurs are also similar to levels where cross-checking occurs, but cross-checking is generally much rarer while block echo is very common, occurring very often when Chip directly follows a block onto sliding tiles.