In many cases, the volume differences can be attributed to the broadcast itself. If it's happening on all channels, it may be an issue with the tuner or the cable/sat box. If you're connected to a cable/sat box, you might see if a reset or refresh can be performed, and this can usually be done on the phone with your service provider's customer service.
recently noticing sound issues. During a program the sound just fades - gets softer, then louder.
Understand volume changes between channels, and when commercials come on.
My wife complains all the time that she has trouble understanding the set. Getting to be an issues with us.