My old phone Huawei G8 (RIO-L02) with Android 5.1 is only used to play music. No SIM card installed and it only has a WiFi connection. The phone frequently plays sound "I am here".
After factory resetting the phone, the sound comes back after a while (about one month). I also have already disabled the location service. The only app I installed is a music player, though I don't think it is related.
Any ideas about which apps play this sound?
This is a feature of Huawei's Android devices known as "Find me" function.
For video demonstration: Huawei P8: Find Your Phone
The feature works by calling the name of the phone then saying "where are you?", then the device will turn on its display, turn on the flashlight, play music, and saying "I'm here".
When the phone is paired to Huawei HONOR Band, it can also be triggered by accessing the "Find my phone" feature from the band (thanks to user Bangyou for additional info).
Depending on the model, the setting may be found on:
Additional sources:
Q & A