Can anybody please suggest a cause/solution?

If I have the TV connected through the Humax and HDMi, I’m getting a picture flash then a loud cracking noise between the end of the programme and the ads, and again when the programme itself restarts.

This does not happen now I’ve disconnected the Humax box and directly plug in via the aerial.

It was happening both on live programmes and recorded programmes both on SD & HD programmes.

I’d be grateful for any suggestions please. The problem first started about 3 days ago, and has not happened this morning since disconnecting the Humax.

Thanks in advance for your help.