Loss of Yaw - New Error Sound from PixHawk

We are only on our third flight with a new 27"-prop quad (U8/135kv). The first flights 2 days ago went very well and tuning was easy. No problems after about 8-10min of flight.

Today we went back up in stabilize mode and after about 1.5 minutes of flight, we started to gradually lose Yaw control (just wanted to yaw to the left harder and harder). We performed a hard landing and checked all the mechanical things. All was well so we rebooted the PixHawk for a second flight thinking a reboot may solve it.

Again all went well for about the 1st minute or so and we started to perform small figure 8’s to test Yaw. This time yaw failed fairly rapidly and it was an even harder landing. Full opposite yaw input only helped slow it for a short time, then nothing helped and a fairly slow uncontrolled yaw was the result.

We are running 8S, Pixhawk is getting power direct through a Castle Pro BEC, I don’t think it was a brownout.

Here are the raw logs from the second flight as well a link to a short clip of a sound the PixHawk was playing immediately after the crash. What error sound is that (we have solid green LED on the PixHawk)?

Thanks for any insight you may be able to provide.

that sound means "command received"
Loock here (min. 0:53)
Probably, about your crash, worked “crash detector” and after this, you can hear that sound continuously.
I find it very useful because for example if you have a crash in a field of tall grass, the sound enables you to find your drone in a few minutes.

Ciao - Giuseppe