TV makes audio hum sometimes

[polhem]

I have my new LG OLED C9 TV connected to my hifi system. All hifi components and the TV's comes from a Monster HTS 2600 power supply.
The TV makes the audio system hum, but only sometimes and whrn certain images are displayed.
The hum goes away if I connect the TV to a different power outlet. However, this is not preferred as the TV connected this way would not be protected from power surges and its power not filtered at all.
I was going to start to debug this situation but I don't know where to start or go about it. I can't unplug the main HDMI from the HTPC to the TV to see if the hum goes away because the hum goes away when just the picture of the TV changes. Can anybody help me where and how to find the problem. Or does anybody know a fix for this? Is there a HDMI hum filter? Should I try to filter the power for the TV in any way more?
I have concluded 3 things:
*The hum only is there when the TV gets power from the same source as the hifi system.
*The hum does not go away when I disconnect the HDMI return audio cable going from the TV to the receiver.
*The hum does not go away when I disconnect the antenna cable from the TV.

My full system looks like:

Antenna:
Wall antenna outlet → Monster HTS2600 Power supply → TV

Power:
Grounded wall outlet → Isolation transformer → Monster HTS2600 Power supply

Audio and video:
HTPC →(hdmi)→ Marantz SR6005 receiver → NAD 3020i amp → speakers
↓ î
→(hdmi)->LG C9 OLED TV →(hdmi)

 

[swechsler]

Sounds like a ground loop. But I'm a little confused. You say the hum doesn't disappear even when you disconnect the TV from the system? so even if the TV is completely disconnected but plugged into power, the hum only goes away if you plug it into a different outlet? How about if you disconnect the antenna from the Monster?

For the time being I'd remove the isolation transformer and the Monster power supply completely from the system and see if that changes anything.

 

[WaynerN]

I agree, remove the antenna routing thru the Monster.

 

[GChief]

but only sometimes and whrn certain images are displayed.

I do not know why, and have noticed it on different brands and models. Some TVs seem to hum when a lot of "white" is displayed. After discussing this with a few people they have noticed this also. Not scientific at all, just an observation.

 

[totem]

Also experienced hum with the wife's Linn system connected to the newer Sony TV
tried everything I could think of only modest success.

 

[sanford12]

I have a LG OLED TV and my stereo setup sharing the same area. Everything is plugged into two different power strips and never had a problem with hum. I think your best bet is what other suggested and try the process of elimination.

 

[polhem]

Thanks for your input guys!

I have made two new obervations:
*The hum does not come from the speakers, they come 80% from the amp itself and 20% from the receiver itself.
*The hum completely goes away when using a non grounded power outlet to power all of the system.

I will try to eliminate things and see if I can find the offending connection.
The tricky thing is I cannot check if the hum goes through the HDMI from the computer to the TV since if I unplug this, I remove the image making the hum itself...

And yes, the hum is generally there when the TV displays a certain amount of white and dark together.

If nothing works, I will connect the TV again to a different outlet since this seems to isolate the TV:s noise from the audio system.