CBC News Network volume on illico HD vs SD

I subscribe to CBC News Network on the illico TV service. When I watch it on the SD channel 18, I can leave the volume set at 28 like most other channels. However, when I switch to HD channel 618, I have to double the volume on my TV to 56 to get the same audio level. Then when the commercials come on they are blasted at high volume and I have to lower the volume, then raise it again when the commercials end. Has anyone else experienced this? It only seems to happen on CBC News Network.