If you are OK with the input side of things and only the output is a concern on approach might be to use a calculated field (Formula Field in recent terminology) to strip out the unwanted characters/source and then report the new field as the output.
However you may also have some input and export Options to consider.
Sorry for the rather generic answer but specifics might somewhat depend on the Monarch version you are working with and whether Classic or DPS.
Pre-preparation of the file may also be an option but could have other effects to consider depending on the approach you are taking for the modelling and data ingestion.
From your description, it sounds like you are using Classic. If so, the options Grant referred to can be found from in the Home->Options menu.
From there, please try the two "Ignore" options.
If this doesn't work or you are using Data Prep Studio, would you be able to provide a sample of the report for testing please?