We just installed a Sharp Aquos 40" and even with the volume all the way up it is hard to hear.

A lot of LCDs can be like this. Is it extremely hard to hear, or just compared to a tube TV?

If it's extremely hard to hear, I would exchange it. But most of the Sharp TVs I've heard are even quieter than others. If the TV is on the wall and you don't want to bother going through the exchange, listen to the display model at the store.

If the display is quiet too, then it's probably just the TV and you'll either have to go with a different set, or get some external speakers. I would recommend going with some external speakers regardless because as I said, most flat panels have poor sound quality.