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?