I'm usually very quiet... maybe a slight gasp or a groan when I orgasm.
I love it when the girl I'm with is loud though!
Sometime that's all it takes to push me over the edge.
My only hang-up is worrying about whether someone else could hear us... Even living together in an apartment I would sometimes worry about how loud my ex was, and it would dampen my mood. But if there's no chance of being overheard, let 'er rip!
