Weird noise when lunging
So I've noticed this noise a few time in the horse. One time when free schooling we were messing around and he was having s whale of a time galloping and broncing and i was jogging around in front of him (he'd been stabled for a few days so was pretty hyped up as hes used to being out) and then he stopped, turned to face me and 'roared'. It was like a snort, but longer and didnt break into the normal snorting noise, just a long monotone grunt roar thing. Honestly sounded like a dinosaur, but he wasn't out of breath or anything but it felt quite aggressive so we stopped.
The second time was today, i was lunging him and he went on one rein fine (again hyped from being in) and then the next rein, he stopped dead, came closer to me and done the weird grunt roars again. Wasn't out of breath and i got on to ride and he was willing and fine.
I dont understand what it is, just worried its the start of a issue i should be looking at resolving but not sure what. Ive googled and it doesn't seem to fit the 'roaring' syndrome as he's absolutely fine when riding,only on the ground he'll do it. I'll try and get a video next time i lunge as he seems to always do it then.