Portacapture X8 : Ultrasonic noise problems

I bought this attracted by the possibility of 32 bit float on a handheld device. Everything ran smoothly until I opened the recordings in a spectrogram.

Using the supplied capsules, you can clearly see ultrasonic noise, steady tones. This happens at all sample rates and bit depths. But there's more, this happens on empty channels too, so you get a hum printed on silence!

I returned this and had a second unit, which has the same problem. I checked online and other users have experienced the same issue. I will return this second unit too, hoping to get it repaired or refunded.

This makes the unit unusable for me and I can't understand how this problem hasn't been addressed by the manufacturer.