I think I know exactly what's going on.... As I have experienced this with certain plugins.... And tried reporting this too...

There is an issue when a plugin (VST2) is trying to open multiple audio ports at the same time when inserted into BIAB instead of Stereo. You can try finding those settings in VST and toggle to stereo or 1&2 outputs at the time when "white noise" is happening. It's unfortunate it wasn't fixed.

I've tested same plugin in new 2025 BIAB as a VST3. No white noise / no issues.