On my Fenix 7S, both the vibration and volume of audio chirps for auto-lap, HR zone alerts, and workout stages (during intervals for example) is so weak that I usually miss the alert altogether. I don't run with headphones, and frequently run in the woods/off-street so pretty quiet environments overall, and I still can't hear them.
For background, I recently upgraded from a Fenix 5S and I have owned many Forerunners of various models over the years. Never had this problem with any of them.
Is this 7S a bad unit, am I missing a setting, or is this just how the 7S model is?