How much hiss is acceptable?

[chaswatson]

I have just obtained a set of Sennheiser RS140 wireless headphones. Despite trying all the settings there is a very faint hissing noise in the background whether through DAB radio or CDs. This is the same with the transmitter in sight or out in the garden. I did not notice this until my wife pointed it out and now it is a bit annoying. The sound source is a Bose. I have turned my WiFi off but that makes no difference. Is there anything else I can try or have I got a lemon?

[ShaunG]

I'm afraid analogue wireless headphones (e.g. Sennheiser RS range) do introduce background hiss to the audio. If you compare a wireless headphone with a wired headphone of a similar price the wired pair will win hands down as far as sound quality is concerned.

The only headphone product we've heard that doesn't do this is the Sleek Audio SA6 Wireless. This uses an uncompressed digital link to transmit the audio and next to nothing is lost. With the music off there is a very slight digital hiss, but it's orders of magnitude better than the old analogue wireless headphones.