Have you used down tuning before in a plugin? Unless you have it loud in monitors or headphones, it’s often very easy to hear your strings acoustically.
If you record a take in Reaper and playback, does it sound ok?
Do you have your audio settings set to listen or your DAW is playing it passthrough. Sometimes you can hear the passthrough in the PC settings, or DAW settings. Like Riek said because you are hearing the guitar’s passthrough at a different tuning it’s more noticeable acoustically. Possibly another track. Maybe test it on a blank mix with 1 track to make sure.
If I record a track and play it back it is completely fine.
I already tried it with the volume loud as fridge and headphones but I dont hear my guitar acoustically I hear it through the headphones.