Toddler Whisper Talking

So this is kind of a new one for me. I have a 3 year old that goes to daycare 3 days a week. He’s gone to the same daycare since he was 1 year old. His speaking and general vocabulary are exceptional. We have 0 issues at home. But at school, his teachers complain that he only whispers to them at a volume that they can’t hear. I figured it was a bit overdramatized, but I saw him do it today at drop off. He is speaking to his teachers at a mouse-level whisper. He isn’t shy around other kids, hasn’t switched classes or anything, and talks to other adults at perfectly adequate volumes. We started practicing the volume game at home (“ok now, we get SUPER LOUD….and then we get quiet, shhhhh”). It hasn’t seemed to make a difference. Any advice on other things we could try to get him to increase volume around his teachers?