Cat Howls while Playing

We recently moved into a new house with our 15 year old spayed female cat and our 9 year old neutered male. Our female seems to be taking really well to the new house. Since moving in, she plays much more than she ever used to, has a much healthier appetite and her coat is looking fuller and shinier than ever before. My fiancé and I have been very pleased with how happy she seems. Now the problem. At night she plays a lot, prancing and frolicking throughout our small home and all the while howling loudly. The first time we heard this howl, we thought she was dying for sure. We both leaped out of bed in a panic only to find her prowling around with her cat toy in her mouth.
   
While the howling is sort of sweet (she never really showed much enthusiasm for play) it is also completely exhausting. I don’t want to discourage her but could really use a good night’s sleep. So my questions: First, why are some cats EXTREMELY vocal while they play? Secondly, is there any hope for a good night’s sleep ever again? Thanks.
   

One: We humans have no idea what causes one cat to play quietly & one to howl like a banshee when pursuing the skin mouse. Nor why old cats suddenly revert to kittenhood & start acting like idiots all over the living room (usually at night). (You must have wonderful open spaces to pursue things in...) I don't think anyone can help you with that.
   
Two: Sleeping. Is your bedroom door a hollow-core door (likely, these days)? If so, it's going to let all the noise through to your bedroom even when closed. Replacing the bedroom door with a solid wood door or a door with sound-deadening insulation may help. Interior or exterior doors can be used; it just matters if they look good & you think the price is worth it. You can also just add a second, solid wood door onto the other side of the doorjamb to open in the opposite direction, leaving the first one in place. This will create a layer of air between the doors that'll further deaden the sound.
   
Solid wood doors can be bought in home stores & numerous places online, or in salvage yards that take houses apart & sell the parts (for a cool antique look).
   
Websites that discuss soundproofing doors:
   
http://www.ehow.com/how_2314248_soundproof-doors.html
   
http://www.soundproofing.org/infopages/soundproofing_doors.htm

I enjoyed your comments, particularly about old cats reverting to kittenhood. It's so true and thanks so much. We actually are planning on replacing all the interior doors since the ones in the house aren't much to look at. Hopefully that will make a little bit of a difference. Thanks again.