I have an AudiaX DGT-201 Transmitter (also sold as an irock! 450FM), for use with a Sony MZ-NH900 HiMD player, mainly in the car. I have noticed that in a typical drive to work, takes about 25 minutes, the sound quality can vary substantially. It seems to fade away, and lose all the highs and lows in the recording, and will then come back to a good sound, before fading away again. This cycle occurs most of the time, but on occasions it does not occur – most confusing. I have tested various configurations – e.g. running the transmitter from the car battery power, different qualities of recordings, making sure that there are no strong FM radio signals near my chosen frequency, but the problem remains. I am using the MD unit on the headphone out setting, rather than line out – I tried line out, but the output was too strong. I have also checked the recordings on the MD unit with both headphones and on a stereo unit (through the line out from the MD unit, into the amp) and the recordings are fine. What could be causing the fading in/out? Could it be related to the car radio, or external interference? The normal radio stations sound fine. Or, could the unit be faulty?