mtb hubs why is his hubs louder but on paper they are the same

Something happening inside the freehub is different. Possible variants that I can think of:

1. One hub has more or different thicker grease on its pawls (or equivalent parts responsible for enforcing the one-way rotation). The grease adds "liquid" friction between the parts, preventing them from smashing as fast against each other with every step of the ratcheting mechanism. Without enough kinetic energy present in pawls to be dissipated as heat/sound, the clicking is not as loud.

2. One hub is older/newer, and its pawls are worn/fresh. Again, the pattern of the pawls striking against their counterparts may affect how loud the sound will be.

3. Hubs have slightly different internal design even if they are marked with the same model name. Their internal components may be from different production batches, or minor revisions can be made without changing publicly visible names of products.

This exact thing happened to me when my wife and I bought new bikes. One bike clicked more loudly when rolling. The bike store employee said it was most likely due to the internal grease amount or location, and would not affect wear or performance.