Well, the noise went away completely when I rotated the tires, but now it's back, and I did some different testing to see when it occurs. Here's the scoop:
When I slow down to 55 mph, regardless of whether it's in gear or not, I get a noticeable whining/groaning noise that vibrates the underside of the car. This continues as I slow down, but as soon as I accelerate, it goes away. Also, if I turn to the right, it goes away until the car is going straight again, and then it returns. It does not occur above 55 mph.
Could it be something in the front suspension? Bad wheel bearing? Bad CV joint? I know my left CV needs replacing, and my tie rods are worn. Do I also have another problem now?
Thanks in advance!

If you want to see scotisha's original thread, look here: viewtopic.php?t=1983