Even when there is nothing running that should normally trigger it, like an video running without any hardware acceleration. While the card isn't exactly heating up at light loads, the power consumption at doing lighter loads like web surfing, Youtube'ing (with h/w acceleration off) or movie watching is definitely higher than with say a HD7950.
Actually it seems pretty typical of AMD's clock profiles. Here's the generic AMD card @Techpowerup
. The Memclock goes to max speeds when you watch video, play games, sneeze.... Is your 7950 a 2GB card? That could make up the difference in power use.