GRUB does not show Arch Linux during startup

I recently installed Arch Linux on my Windows partition via USB boot.

But GRUB still shows Windows during startup on the partition. I already tried reconfiguring the grub.cfg:

$ sudo grub-mkconfig -o /boot/grub/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.4.0-57-generic
Found initrd image: /boot/initrd.img-4.4.0-57-generic
Found linux image: /boot/vmlinuz-4.4.0-53-generic
Found initrd image: /boot/initrd.img-4.4.0-53-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
Found Arch on /dev/sda4
Found Ubuntu 14.04.5 LTS (14.04) on /dev/sda9
done

It says it would find Arch, but during the startup there is still Windows displayed.

This is how my partitions look currently:

$ sudo parted /dev/sda print
Model: ATA SAMSUNG MZ7TE256 (scsi)
Disk /dev/sda: 256GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:
Number Start End Size File system Name Flags 1 1049kB 1050MB 1049MB ntfs hidden, diag 2 1050MB 1322MB 273MB fat32 EFI system partition boot, esp 3 1322MB 1456MB 134MB Microsoft reserved partition msftres 4 1456MB 104GB 103GB ext4 Basic data partition 9 104GB 125GB 21,0GB ext4 Ubuntu14 5 125GB 157GB 31,5GB ntfs Basic data partition msftdata 6 157GB 160GB 3000MB linux-swap(v1) 8 160GB 256GB 96,4GB ext4 7 256GB 256GB 128MB bios_grub

On partition 8 is Ubuntu 16, which I mainly use, and on which the GRUB files are, too.

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