A while ago I stumbled upon a low-level adventure in which a band of goblins has a giant mechanical turtle and terrorizes/scares the locals with it. I think it must have been a D&D/Pathfinder 3.X book, but my google-Fu is too weak to find it.
It is possible that you are remembering Goblins' Return and Heart of the Enemy, SJS1 and SJQ1, respectively, from Spelljammer. I can't be certain, as I only recall these modules on the shelf of the FLGS I managed in the late 80s (1987-89,1990).
In Spelljammer, the DragonTurtle Ship, or Turtle Ship, is a "gammraoid" that fits the description. The two adventures, for 7th-11th level characters (not quite "low level" but not paragon or epic either), explore goblinkin's return from a banishment (after the Unhuman War).
I cannot think of another tie-in, à la Earthshaker! for D&D (module CM4, BECMI), where a mechanical foe of anthropomorphic design is run by Goblins.