When someone or something is causing suspicion, it means that there is a feeling of doubt or mistrust being aroused. A few synonyms that can be used for this phrase might include "raising eyebrows," "casting doubt," "provoking concern," "arousing skepticism," "inspiring uncertainty," or "inciting wariness." Depending on the context and tone of the situation, some of these synonyms may be more appropriate than others. For instance, "arousing skepticism" might be a more diplomatic way of expressing suspicion in a professional setting, while "raising eyebrows" might be a more colloquial and casual way of expressing it among friends.