Well, I dont wanna start a debate, but the official website of GNU indicate that the "g" in GNU isn't silent.
So it depends on whether you want to pronounce it "properly" or as it was intended.
The name “GNU” is a recursive acronym for “GNU's Not Unix!”; it is pronounced as one syllable with a hard g, like “grew” but with the letter n instead of r.
Well, I dont wanna start a debate, but the official website of GNU indicate that the "g" in GNU isn't silent.
So it depends on whether you want to pronounce it "properly" or as it was intended.
https://www.gnu.org/gnu/pronunciation.en.html