truck vs sound truck

truck and sound truck both are nouns.

Word	Noun	Adjective	Verb	Adverb
truck	Yes	No	Yes	No
sound truck	Yes	No	No	No

As nouns, sound truck is a hyponym of truck; that is, sound truck is a word with a more specific, narrower meaning than truck:

truck (noun)	sound truck (noun)
an automotive vehicle suitable for hauling	a truck equipped with a loudspeaker and used for advertising
a handcart that has a frame with two low wheels and a ledge at the bottom and handles at the top; used to move crates or other heavy objects

truck (verb)	sound truck (verb)
convey (goods etc.) by truck