The only time I've heard a sound like it is on the labour ward. I accept that when people are shifting heavy weights, they often grunt/groan with the effort.
But THIS groan really does sound like a woman in the last stages of labour. Loads of people look at each other when he starts up because it is so loud and the groans go on so long. He does it for most of the hour he's working out.
Is he being unreasonable? AIBU to feel like asking him to pipe down. Or shift lighter weights because he appears to be putting himself under incredible strain.