Comment # 11 on bug 1090760 from Takashi Iwai

(In reply to Thomas Moringer from comment #9)
> With version Leap 42.3 this sound behavior did not occur.

OK, that's a good information.

Could you try to install openSUSE Leap 42.3 kernel you've used onto Leap 15.0
system and retest with that kernel?  You can install the old kernel-default.rpm
via "zypper in --oldpackage kernel-default.rpm", for example.

If the problem doesn't happen with Leap 42.3 kernel but only with Leap 15.0
kernel, we can try to narrow down further.