Does the stock impala radio adjust volume to the current driving conditions. I have noticed that in my impala the radio seems to adjust by itself when i driving.

Anyone know?

well its easy to figure out if the radio in question does that or not. on the radio there are buttons that say "auto vol". if they are there, then it does, if not then no.

All impalas have auto volume or speed compensated volume. Press auto vol (bottom right on radio) repeatedly to cycle through low med high and off. I think on 03's and up, they updated the radio a little (not noticeably) and the amount of volume the auto vol adds is a little more reasonable. Low is usually the most natural choice.