Its to exaggerate the weight of something and give you the impression its heavier then it really is. Something I've found funny is when I've been in a mixed gender gym it happens more but in a completely guy gym I hardly ever hear it lol.
sometimes the guy might want to try to impress other guys though, sometimes the noise is over the top. I've even seen an occassion where the employer had to tell the man to stop screaming
Its not something heavy, its something your body is trying to stop you lifting, so you need to put in everything you have left inside you to be able to lift it, which suddenly results to a load grunt, it hurts to lift heavy weights your body don't want to lift, so some sort of expression is a reaction, I know it can be annoying, but there's no stopping it, even if we were asked to, it would be impossible to reduce, its just what happens when your maxing your strengths out, and if you tried to do all the press ups you could possibly do, then do one more, you would grunt also, its a reaction to the effort that gets put in,x
If I'm lifting something insanely heavy, I'm really not concerned with making noises. It's easy to stroll along on the treadmill wondering why they're making all that noise vs. actually struggling to get the weight up.
It's a gym you're in and that's just part of the territory.
I son't do it very loud but to me it's a mental thing. Kind of like a ritual when I'm lifting heavy weights (close to one rep max). It's not always a way to get girls' attention like others said at least for me since there's usually no girls at my gym. I actually do it without even thinking about it.
Some also do it for adrenaline, but that is only when someone shouts out loud before a lift not just a grunt and some (or most, I don't know) do it for the attention.
Same reason people make crazy sounds in martial arts. It provides a power boost. Not sure how it works, but it does.
Idk when I lift weights I usually have music in so I don't really notice but I've heard from my buddys that I can get pretty loud when I'm really pushing it, when I'm not listaning to music I don't at all though... apparently one time when I was going for my record I was blastin music and my buddy told me right before I got to the top I yelled out "YA BITCH?!" and the whole gym looked over and I was getting harsh dirty looks when I was done
Lol, they're so dramatic! They used to do that at the gym I worked at all the time! I thought it was funny. Sometimes the grunts were really hot and I'd just tell myself "I'm gonna make a man grunt like that one dy :)"