Just had a realisation. The noise is not interference in the actual inbound Audio interface signal. 
What is happening is when plugged in in Multitrack mode, and at 44.1kHz, the tablet/software is outputting a noise through the recorder's speaker, which is then picked up by the microphone - hence the noise in the recording. However, it is not feedback.
If I turned the monitor volume down to zero, the recording itself is noise free. If I plug in headphones, the noise can be heard over them, but at least doesn't reach the microphone. The H6 has a setting "direct monitor off", which seems to fix this, at the expense of monitoring. This is going to be my solution for now.
I have also noted that if I start with a clean recording, and play that back through the H6 (headphones or speaker) I get the noise. So it is a product of sending audio from the tablet to the H6 (either as a monitor signal or playback).
I can live with this. However, it is still the case that this problem is only apparent when at 44.1kHz - 48khz and 96kHz work fine. But while that is a solution for USB Audio Recorder PRO, Audio Evolution Mobile only offers me 44.1kHz.
Sorry to have gone on about this, but I've actually found it quite interesting.
What is happening is when plugged in in Multitrack mode, and at 44.1kHz, the tablet/software is outputting a noise through the recorder's speaker, which is then picked up by the microphone - hence the noise in the recording. However, it is not feedback.
If I turned the monitor volume down to zero, the recording itself is noise free. If I plug in headphones, the noise can be heard over them, but at least doesn't reach the microphone. The H6 has a setting "direct monitor off", which seems to fix this, at the expense of monitoring. This is going to be my solution for now.
I have also noted that if I start with a clean recording, and play that back through the H6 (headphones or speaker) I get the noise. So it is a product of sending audio from the tablet to the H6 (either as a monitor signal or playback).
I can live with this. However, it is still the case that this problem is only apparent when at 44.1kHz - 48khz and 96kHz work fine. But while that is a solution for USB Audio Recorder PRO, Audio Evolution Mobile only offers me 44.1kHz.
Sorry to have gone on about this, but I've actually found it quite interesting.