Beep while building RAID 1 array

I’ve built a NAS system using a supermicro superchassis. This chassis has Supermicro CSE-SAS-733TQ backplane supporting 4 hotswap bays.

Everything runs OK. I run a fresh debian 10 install. Now I tried to create a RAID 1 array of the two WD Red disks using mdadm. As soon the building of the array starts the system starts emitting small beeps. I located this must come from the backplane area. I’ve swapped the disks arround because I was afraid of disk failure but that seems OK.

I suspect this is a something of a controller warning. Because the array is being build.

Is somebody familair with this behaviour? I think the beep might stop after the array is successfully built. Any advise is appreciated.

System specs.

• SuperChassis 721TQ-250B
• backplane CSE-SAS-733TQ
• Asrock H370M itx/ac
• Intel i3 8100
• 2x WD RED 4TB (storage)
• 1x WD Black Nvme ssd 250GB