My zone headphones troubleshooting

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

It should be in the TV audio settings. What is the make/model of the tv?

Did you connect the base/transmitter piece to the AUDIO OUT jacks on the back of the TV ? The radio you are listening to is the built-in FM radio/tuner. You need to connect the transmitter to an audio source (TV, PC, CD/DVD player, etc.) to receive sound from that source.

Hook up the transmitter piece that came with the headphones (the one where you store and charge the headphones) to the audio output on the back of your TV.

Your receiver has Zone-2 functionality. For Zone-2, it has both speaker (powered) output and pre-out line outputs. According to Yamaha FAQ, these pre-out outputs are independent on the main volume settings. So if your wireless headphones have their own volume settings, you can change the volume independent on speakers volume.

If you want same volume for speakers and headpohones, use the PRE-OUT FRONT outputs on the back. If you want different volumes (and listen to headphones even with speakers muted), use ZONE-2 OUT outputs on the back.

Just found this and it worked! Hope it does for you as well:
There should be a button on the DVD remote control with a headphone symbol on it. Make sure the headphones are turned on(red indicator on earpiece) and push the headphone button on remote. The headphones will only work in the back seats of the vehicle. Once you have audio to the headphones, you should be able to hit the AM/FM button on the radio and listen to the radio while back passengers use the headphones for video.

Hello, IF your tv is capable of using headphones it will have a little jack with a head phone symbol over it or under it most likely. IF not you can buy a home theater system which would hook up to your tv and some of these have an option to hook up headphones or even ipods and usb devices. 
the greek

u have to split the signal by having both the tv and the headphones getting the input,as you're probably only have the audio cables going to the headphones.You need an audio splitting cable (it has 4 malle connections) so you can put 2 in the tv and 2 in the headphone base.

i think its a factory setting you cant change. you cant listen to radio without headphones.