a dull explosive sound made by or as if by a laboring engine
chug chugchug chugchug mmmoooosh
sound of a steamroller (Diggers go by Steve Light. All caps in the book chug chugchug chugchug MMMMOOOOSH)
chugGA chugga chugga chugGA chugga chugga CHOO CHOOOOOOO
steam engine or train. from this book: 
Click here for more train sounds
Search tips:
- Fewer searchterms (eg. cat will yield more results than cat sounds)
- Try synonyms (eg. if saber does not give you results, try sword, cutlass or blade)
- Truncate (eg. walk will give more results than walking because it returns everything that has walk in it including walked and walks)