Question about RØDE Ai-1

Hello, I have ordered the Rode AI-1 in conjunction with my HL4100 earphones. However, I have a background noise on the InEars. Of course, I would never connect the 300€ InEars to my PC without a sound card, but they don't have any noise... I also have a jack adapter between the hearing aid and the AI-1, which shouldn't affect anything...! I have also read a lot about how it is with professional headphones... that they have/need a certain Ohm value or that a preamp is needed. And the Rode is (I think) not a bad interface for its price... what am I missing? Can anyone help? Technical data Hörluchs: Note: Suitable for professional use only. Sensitivity at 1 mW: 118 dB SPL Impedance at 1 kHz: 22 Ohm Frequency range: 20 Hz - 20 kHz Maximum output: 127 dB SPL Distortion factor at 94 dB SPL: 0.2 Distortion factor at 100 dB SPL: 0.2 %. Technical data AI-1: Gain Range - 60dB (with firmware version 1.3.1) Bit Depth - 24-Bit Sample Rates - 44.1kHz 48kHz 88.2kHz 96kHz 48V Phantom Power - Yes Simultaneous I/O - 1 x 2 Number of Preamps - 1 Direct Monitor - Yes Bus Powered - Yes OS Requirements - Mac OS10.10 or later Windows 7 or later Power - USB bus-powered