Trunk rattling?

The trunk of my car is loose and constantly rattles (no sound system involved). I've emptied it and even checked to make sure it wasn't the spare tire or anything in the tirewell.
What can I check on or tighten to fix this problem?
THANKS!

You've tightened down the spare and the jack. That makes it tough because that is usually the problem. Could it be the muffler or taillpipe? Grab the tail pipe and give it a good shake. It could be loose hitting the bottom of the trunk. Is the back rest of the rear seat tight? If all else fails you could get a can of sound deadener and coat the inside of the trunk. That might help some. btw what is the make and year of your vehicle?

It's a 98 Ford Contour, thanks--I'll try your tips!