Sony wireless headphones

No it isn't normal. This is a set that you plug into the television and it transmits the signal to the wireless headphones. It sounds like the transmitter unit is picking up interference. We can test it! The headphones can be connected directly with a wire. Try that on the television earphone jack, or on a cellphone, a radio, MP3 Player or a computer audio jack. If the audio is clear, with no hiss, then you know the problem is the transmitter unit. Move it as far away as the wires allow from the television and anything electronic.

It is advertised here on Amazon and the diagram shows how it can be connected, 4th image down on upper left.

5-in-1 Wireless Headphones Headset MH2001 MP3 MP4 ...

Amazon.ca https://www.amazon.ca > Wireless-Headphones-Heads...

5-in-1 Wireless Headphones Headset MH2001 MP3 MP4 PC CD DVD Audio TV FM Radio-Listen to Music, Chat Online & Monitor Other Rooms! : Amazon.ca: Electronics.
More here regarding the hissing sounds

https://www.google.com/search?q=mh2001+wireless+headphones+hissing+sound

A number if things can be wrong with it, from the audil preamp to the the audio amplifier. Even as simple as a bad volume control. Does the actual noise change patterns when you move the volume?

The static you're experiencing with your Sony wireless headphones can be caused by various factors, including interference from other electronic devices, radio frequency congestion, and distance from the transmitter. Here are some things you can try to minimize the static: Move the transmitter closer to your headphones: The closer your headphones are to the transmitter, the stronger the signal will be and the less static you will hear. Reduce interference: Try turning off any other electronic devices that may be causing interference, such as microwaves, wireless routers, and cordless phones. If possible, move the transmitter away from these devices. Change channels: Some wireless headphones have multiple channels to choose from. Try changing the channel to see if that reduces the static. Check the batteries: Make sure the batteries in your headphones are fully charged or replaced if necessary. Reset the headphones: Sometimes resetting the headphones can help eliminate static. Refer to the user manual for instructions on how to reset your specific model. Contact Sony customer support: If none of these solutions work, you may want to contact Sony customer support for further assistance or consider getting a replacement if your headphones are still under warranty.

Possibly interference from another electrical source. This can be compounded by high gain or the use of a distortion pedal. Try moving the amp to the middle of the room or away from things like appliances, lighting dimmer switches computer, tv etc.
Hope this helps.

Well I just plugged into the cable box and that worked. On my old tv as well as my newer one the only audio out was an optical I had bought an optical splitter (one input for my sound bar and the other one to the optical to Rca) and an optical to rca for the headphones. This allowed me to use the headphones on all things going through the tv. For some strange reason it no longer works that way (just got my new tv this week). I bought all pieces on Amazon for a nominal cost. I'm going to doublecheck all connections again tomorrow.