boombox
(Afaik, an RPG-7 round is usually a HEAT round, which usually does the opposite of detonating inside of an enemy. What you're thiking about are common APCHE projectiles, with set fuses depending on armor thickness. An APDSHE round was developed for the Tiger II, but never fielded. Also this is the third time I write this because my internet keeps shitting itself.)
From within the system, the same effect of randomness can be seen in an enourmous patch of space, though, instead of anything appearing, there is a ripple that hits the planet like a wave, scattering transmissions ever so momentarely. However, the worm notices such a ripple, and immediatly begins to dig downwards.
Upon its path, it seems to swallow its own plating, turning into a much longer and sleeker creature, gaining speed conforming to the design changes, like an extremely fast paced directed evolution. Soon it heads to the surface and erupts from it with violence and strenght, as if it was shot from a cannon it soars into the sky.
After a few seconds of ascendency, almost reaching its peak, a series of detonations and contractions can be seen emanating sequentially from its bottom upwards, as then a large tongue-like apendex shoots from its mouth, like a second fire from the earth, it acquires even more height, before grapling into something.
Miraculously enough, it seems to have hooked itself to... thin air? Whatever it has attached itself to is either obscured by the clouds or can't even be seen, nonetheless, it pulls itself up with the tongue-like apendex, and seemingly starts to lose size, before leaving the atmosphere of the planet and its surroundings in great speed, and dissapearing into nothingness.
The trooper within the ship, which stood still on a corner, watched the whole event unfold, not with its eyes but with the connection that it had to the being, after such a strange phenomena, it readies itself for disembarkment.