Shmot 9:23 uses the word "Kolot", which means "noises" or "voices". I'm assuming, therefore, that this means thunder as this is a "noise".
Scientifically, there is no thunder without lightning, first. As I understand, the Hebrew word for lightning is "Barak". We don't see this word mentioned anywhere in the story of the plage of hail.
So was this another part of the miracle of this plague in that there was thunder without lightning?
Romamos Kel - Alshich on Sefer Tehilim says that the noise of the Barad were noises from the Olam Ruchni, out of this world. Thus the lack of lightning was not an additional miracle as the thunder was not regular thunder.
There seems to be differences of opinion whether the "sounds" refers to thunder, and whether there was lightening as well. See the Pirush H'kesav V'hakabala on Exodus 9:23 in which he cited some commentaries who are of the opinion that the "sounds" refer to thunder, and the fire refers to lightening. He however, is of the opinion that it does not refer to thunder and lightening.
