Successfully solved with this code in /etc/config.scm:

(operating-system
...
  (kernel-arguments '("modprobe.blacklist=pcspkr,snd_pcsp"))
)

# guix system reconfigure /etc/config.scm
# reboot

PC speaker no longer beeps. Thank you!
I think it's a luck, cause from here 
https://github.com/alezost/guix-config/blob/469db8060235cc6bb7501cfb798f29ede3cc21e6/system-config/os-main.scm#L29 <https://github.com/alezost/guix-config/blob/469db8060235cc6bb7501cfb798f29ede3cc21e6/system-config/os-main.scm#L29>
I've got names of kernel modules, so that not only pcspkr, but also snd_pcsp needs to disable
and from here
https://gitlab.com/pkill-9/guix-config/blob/master/system-config.scm#L123 <https://gitlab.com/pkill-9/guix-config/blob/master/system-config.scm#L123>
I've got that simple line that not breaks my config.scm syntax.
Still do not know why guix does not find `(use modules  (al utils))` module and how to get guile modules work.


Mar 16, 2019, 4:46 PM by znavko@tutanota.com:

> You know, Tobias! Just for experiment I've add (al utils) and guix cuss out:
>
> (use-modules (gnu) (gnu system nss)
>              (gnu system locale) ;;for locale-definition
>              (gnu services desktop)
>              ;;(gnu services dns) ;;for dnsmasq
>              (srfi srfi-1) ;;for remove function
>              (gnu services networking) ;;for remove ntp
>              (gnu services avahi) ;;for remove avahi
>              (gnu services xorg)
>              ;;(gnu services databases);;for postgres
>              (gnu packages admin) ;;for wpa_supplicant
>              (al utils)
> )
>
> # guix system reconfigure /etc/config.scm
> guix system: error: failed to load '/etc/config.scm':
> ice-9/boot-9.scm:2803:6: In procedure resolve-interface:
> no code for module (al utils)
>
> What is wrong here? How to use guile modules?
>
>
> Mar 16, 2019, 4:00 PM by > somebody@not-sent-or-endorsed-by.tobias.gr <mailto:somebody@not-sent-or-endorsed-by.tobias.gr>> :
>
>> Zvavko,
>>
>> znavko wrote:
>>
>>> # guix system reconfigure /etc/config.scm
>>> /etc/config.scm:97:26: error: comma-separated: unbound variable
>>> hint: Did you forget a `use-modules' form?
>>>
>>
>> […]
>>
>>> Mentioned github page has no any use-modules string that can help.
>>>
>>
>> Look again.  From system-config/os-main.scm:
>>
>> (al utils)
>>
>> And indeed, guile/modules/al/utils.scm has:
>>
>> (define (comma-separated . strings)
>> "Return string by concatenating STRINGS with commas."
>> (mapconcat identity strings ","))
>>
>> You can copy the definition to your own configuration, or just replace it with the (trivial) MAPCONCAT call directly, or just use a comma-separated string to begin with.
>>
>> Kind regards,
>>
>> T G-R
>>
>
>