I'm also a mechanical engineer. Qualified to the same level although I don't pay the imeche fees anymore so don't have the letters after my name.
I completely disagree with you I'm afraid. Engineers often do make or fix things, I used to make lots of prototypes, I've installed new equipment, I've been out fault finding.
A sound engineers job could definitely be described as engineering. They are diagnosing sound problems, manipulating acoustics, manipulating sound waves. They are applying physics to produce a product. There's a fair amount of art in what they do as well as science. Maybe they're closer to a BSc or maybe Ba qualified engineer rather than a BEng but they certainly deserve the title engineer far more than plenty of people who I deal with (project engineers especially).