Two common problems here:
1.
Different volumes for each channel. This is something that the provider (Bell) can adjust at the head end for each channel, but the engineers really can't be bothered. If there are one or two channels that are really too loud, then by all means,
complain to Bell.
2.
Loud commercials. Commercial producers compress the audio on purpose so that their commercial gets attention from the viewers because it's louder. Kinda like how modern music has turned into a compressed mush to get better airplay on radio stations compared to music produced a decade ago. Looks like they got your attention and their tactic worked! Complain all you want, but commercials=money for television/cable channels, I doubt anything going to change in this regard until enough people put pressure on the advertisers.
Part of the problem is, they're reprocessing signals from a variety of different sources, and its difficult to keep all the levels set similarly. It gets even more complicated when your
TV provider (Bell/Rogers) has to do program substitution.
The engineer needs to
make adjustments for each channel's audio level, unfortunately it involves time and effort to perform these adjustments. A good retired audio friend of mine is paid by a major cable TV provider to listen in on all their channels with his scope and analysis equipment, and reports any deficiencies to the engineers. He gets to watch TV and get paid for it!
