Were dinosaurs able to produce other sounds aside from hissing noises like modern day reptiles aside from hadrosaurs (namely parasaurpholos)? Is there any fossil evidence that some would have a syrinx like bird since their skeletal systems are closely related?

Well crocs are capable of quite a variety of noises and are not just limited to hisses, so we wouldn't expect dinosaurs to be especially limited. I'b be quite surprised if some of the species closer to birds, or some of the more social ones were not capabale of a great range of calls and sounds, but as you note, there's no real evidence for anything like syringes or a particaulr reason to think any dinosaurs had them, though that doesn't rule it out.