I think this just occurs when chopping down trees or mining which makes a lot of noise attracting the local fauna to come investigate the invading Viking.

Nighttime you can come across enemies more frequently and they sometimes travel in little packs of like 3-4 or so depending on the environment.

Imo Valheim could use like... 1-3 difficulty levels. 1 being easy without the extra aggro of making noise and invasions, 2 being what we have and 3 being something worthy of true Vikings who want that extra challenge with perhaps increase spawn rates / density, slightly higher rate of starred enemies and starred enemies can show up during Invasions rarely.

I also want to see a lot more places of interest the player can stumble across when exploring - perhaps some could be bound to the difficulty you play on as well like a ruined keep in plains occupied by fulings who killed the previous occupants.