Some Headphones have an inherent hiss noise when they are connected to my wireless sennheiser EK 300 IEM G3 receiver. It seems to be a problem particularly with high-end IEMs which are highly sensitive and have very low impedance. The hiss is constant regardless of whether or not the transmitter is turned on or the volume knob is turned up
Music - Sennheiser - ew 300 IEM G3 In-Ear Wireless Monitor System
Answers & Comments
Hiss is a problem of statistical noise in electronic devices due to the laws of physics plus circuit design.
One thing to do is to improve the signal to noise ratio (SNR) by properly setting gains. It is POSSIBLE that the IEM's you are using are too low impedance for the receivers resulting in you having to use excessive gain at the receiver. Your receiver gain control should not have to be above 60% of the way up. If you are above that, the ear buds are probably lower impedance than the receiver is designed for... and remember the manufacturer will LIE on the capability of the thing they are trying to sell.
The receiver is speced at 32 ohm drive... IF your ear buds are less than that impedance, they are NOT suitable. Conversely if they are too high, thaat will ALSO cause you to turn up the receiver gain too much and result in poor SNR.
You want to make sure the transmitter is being driven at line level so receivers get adequate input audio so gain doesn't have to be run too high.