Quiet on Partial Inclines.

I drive a manual '96 Plymouth Neon that has about 161K. I'll relate my question to a washing machine. When your washing machine starts the spin cycle, you'll know if it's not balanced by the horrible knocking sound it emits. With my car, the faster I go, the louder she gets. It's just like the washing machine sound, except it's a lot faster and is more of a consistent humming nature. I noted that whenever I drive on a partial incline (when the right side of the lane is a bit higher than the left), she runs QUIET like she's supposed to. But the second it's flat ground, she's back to being loud. My first thought is to have her realigned. Any other thoughts? THANK YOU! :OD