Weird noise after editing wavs in cubase ai

I’ve recently updated to Cubase AI. Up to now when I’ve recorded audio into channels in Cubase I have often edited those wavs in Audacity (removing unwanted background sounds and a bit of compression etc). In the earlier Cubase that was fine. Now I find that after editing wavs in Audacity when those wavs are played in Cubase there is horrendous hissing and white noise. In isolation the wavs are perfect. The bit rate and sample rates are identical. What is causing this? Anyone have any ideas?

If you import an audio file into Cubase that was not exported from Audacity, does the horrendous noise appear then?
What options do you have when exporting a .wav file in Audacity?

Can you expand on what you mean by “in isolation”?