Why would a guy be loud but when you walk by they tend to whisper?

A guy might be loud in a group setting to assert himself, seek attention, or engage with friends, but when you walk by, he may whisper out of shyness, curiOSity, or a desire to avoid drawing your attention. This behavior can also indicate that he feels self-conscious or wants to keep his conversation private. Essentially, it's a mix of social dynamics and personal feelings that can influence how he behaves around you.