Mark0
This happens with all HD channels an SD local inserts. It even happens on low budget local OTA channels (locally Fox 19 WXIX is a culprit). The problem is the way SD and HD content has the audio set. The HD channels have a digital (DD 5.1) soundtrack which has a low level base line audio. This gives the channel a lot of "head room" for those bone-rattling action scenes and loud parts...when people are talking, it sounds like people talking. When helicopters are flying overhead, it is VERY LOUD and the DD5.1 track will do that.
When the local originated commercial inserts are placed into a channel, they are generally up-converted SD content which has a much higher base line audio level since it is usually standard analog sound. This means that the sound is a LOT louder than the average sound on a digital/HD channel.
The solution is a fairly expensive piece of equipment that equalizes the sound levels. The major technical issue is how to allow the commercials to have equalized sound while at the same time allowing the actual programs to have their full dynamic range (Loud stuff loud-soft stuff soft).
I have a dynamic range compressor on both my TV and my Yamaha DD5.1 receiver but I do not like to use them since it affects the sound for everything, not just the offending local insert commercials.
See ya
Tony