growth rate vs rate of growth

growth rate and rate of growth both are nouns.

Word	Noun	Adjective	Verb	Adverb
growth rate	Yes	No	No	No
rate of growth	Yes	No	No	No

As nouns, growth rate and rate of growth are synonyms defined as:

growth rate and rate of growth: the rate of increase in size per unit time

growth rate (noun)	rate of growth (noun)
the rate of increase in size per unit time	the rate of increase in size per unit time