A recent article in Nature suggests they did not roar. Their voice box is more like birds.They probably made some sound, but not like the ones we hear in movies such as Jurassic Park. Some dinosaurs have a head shape that was probably designed to project sounds a long distance, so there is good evidence they made sounds. We may never know which kind since those structures, like a voice box, are not preserved well in fossils.
This is just a guess, but maybe the sounds produced could have been recorded in tree sap if the conditions were just right. If that happened and the tree sap became a fossil, we could play back the sounds today.