Can anyone help me with this frustrating volume issue?

We often find we're watching a show on Sky Q and the volume will keep subtly becoming quieter then louder throughout. We end up having to turn it up or down every few mins to be able to hear speech in a show, or to turn it down as it suddenly gets louder again.

Is not an issue on all channels or all shows. Hard to identify if it's an issue on specific channels or just specific shows, or more random than that.