During Matan Torah, the shofar was heard by the entire nation but who blew it? Was it Moshe? Angels? The text does not specify. Is there midrash to address this?
Well, my hunch is correct, at least from one Acharon!!
See Or Hachayim on Shemot 19:19 - "Moshe spoke and God answered him in a voice". According to Or Hachayim, "the voice" refers to the voice of the shofar.
(Keep in mind that this is just one of many interpretations of what the term "voice" is.)