One small trick you can sometimes use is to find the right "spot" in a noisy situation. This weekend I played/sang with a group of friends in a bar we used to play regularly, but had not visited for some time.

When we took up our positions in the accustomed place, at one end of the room, everyone mentioned they couldn't hear themselves like they used to. Something had changed -- a piece of furinture moved, a new ventilation system, or something. I found that by moving to the other end of the group, a distance of about seven feet, and getting the surface of a bare wall behind me, my singing volume seemed to increase significantly.

Of course you don't always have the luxury to experiment, but it's worth looking for the "sweet spot" whenever possible.