pcspkr not producing sound using beep (Proxmox): debugging ideas?

I'd like to use the beep command for simple diagnostics for my headless Proxmox-machine in case networking fails. While the BIOS-beep and even the GRUB-beep work fine, issuing beep via SSH does not produce the expected sound; instead, a short "clack" -- like plugging in speakers -- and a command-corresponding pause is all I get.

Steps taken:

• I installed a known working pcspkr (hardware) and confirmed installation via activating the BIOS-startup-beep.
• I confirmed availibility to the OS by activating the GRUB-beep in /etc/default/grub.
• I installed the beep-package (beep 1.4.9), added a udev-rule /etc/udev/rules.d/70-pcspkr-beep.rules (ACTION=="add", SUBSYSTEM=="input", ATTRS{name}=="PC Speaker", ENV{DEVNAME}!="", TAG+="uaccess"), added the corresponding user to the input group (sudo usermod -aG input USERNAME); un-blacklisting pcspkr is not necessary under proxmox.

Running beep does not produce any error message. beep --debug shows:

beep: Verbose: beep_drivers_register 0x5568bdb98600 (console)
beep: Verbose: beep_drivers_register 0x5568bdb98660 (evdev)
beep: Verbose: evdev driver_detect 0x5568bdb98660 (nil)
beep: Verbose: b-lib: opened /dev/input/by-path/platform-pcspkr-event-spkr as 3
beep: Verbose: beep: using driver 0x5568bdb98660 (name=evdev, fd=3, dev=/dev/input/by-path/platform-pcspkr-event-spkr)
beep: Verbose: 1 times 200 ms beeps (100 ms delay between, 0 ms delay after) @ 440 Hz
beep: Verbose: evdev driver_begin_tone 0x5568bdb98660 440
beep: Verbose: evdev driver_end_tone 0x5568bdb98660
beep: Verbose: evdev driver_end_tone 0x5568bdb98660
beep: Verbose: evdev driver_fini 0x5568bdb98660

The kernel module is loaded and active:

$ lsmod | grep pcspkr
pcspkr                 16384  0

Since there is no sound card in the machine, ALSA / pulseaudio are not installed. I blacklisted snd_hda_intel to be on the safe side.

Questions I have:

• Is it possible for the pcspkr to be muted (like many people seem to have issues with)? Since there is no sound card, installing alsa-utils does not help with this possibility.
• Any way I can manually issue a tone to be played by the pcspkr, i.e. ruling out a beep-issue?
• How to diagnose further?

I found a similar issue on the ArchLinux-forums.

Thanks a lot!