ffmpeg concats .VOB files - sound missing?

I use ffmpeg to concat my .VOB file. It merges them Ok. But there is NO sound at all after combining:

ffmpeg -i 'concat:VTS_01_1.VOB|VTS_01_2.VOB|VTS_01_3.VOB|VTS_01_4.VOB|VTS_01_5.VOB|VTS_01_6.VOB|VTS_01_7.VOB' -acodec copy -vcodec copy combined.mpg

Any ideas?

EDIT:

My terminal output:

ffmpeg version 3.4.4-0ubuntu0.18.04.1 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
  configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  WARNING: library configuration mismatch
  avcodec     configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, mpeg, from 'concat:/home/lau/Desktop/merge/VTS_02_1.VOB|/home/lau/Desktop/merge/VTS_02_2.VOB':
  Duration: 00:40:34.30, start: 0.287267, bitrate: 7056 kb/s
    Stream #0:0[0x1bf]: Data: dvd_nav_packet
    Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, top first), 720x576 [SAR 64:45 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:2[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 320 kb/s
    Stream #0:3[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
[mpeg @ 0x55aa4a6e7180] VBV buffer size not set, using default size of 130KB
If you want the mpeg file to be compliant to some specification                                 
Like DVD, VCD or others, make sure you set the correct buffer size                              
[mpeg @ 0x55aa4a6e7180] ac3 in MPEG-1 system streams is not widely supported, consider using the vob or the dvd muxer to force a MPEG-2 program stream.                                         
Output #0, mpeg, to '/home/lau/Desktop/merge/combined.mpg':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: mpeg2video (Main), yuv420p(tv, top first), 720x576 [SAR 64:45 DAR 16:9], q=2-31, 25 fps, 25 tbr, 90k tbn, 25 tbc
    Stream #0:1: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
Stream mapping:
  Stream #0:1 -> #0:0 (copy)
  Stream #0:3 -> #0:1 (copy)
Press [q] to stop, [?] for help
[mpeg @ 0x55aa4a6e7180] Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly
[mpeg @ 0x55aa4a68b900] New subtitle stream 0:4 at pos:125679630 and DTS:189.367s
frame= 6805 fps=0.0 q=-1.0 size=  193188kB time=00:04:32.12 bitrate=5815.8kbits/s speed= 544x   frame=12253 fps=12253 q=-1.0 size=  397130kB time=00:08:10.04 bitrate=6638.8kbits/s speed= 490x frame=18133 fps=12088 q=-1.0 size=  589072kB time=00:12:05.24 bitrate=6653.9kbits/s speed= 483x frame=24516 fps=12257 q=-1.0 size=  787674kB time=00:16:20.56 bitrate=6580.6kbits/s speed= 490x frame=30390 fps=12155 q=-1.0 size=  984682kB time=00:20:15.52 bitrate=6636.3kbits/s speed= 486x frame=36349 fps=12116 q=-1.0 size= 1183140kB time=00:24:13.88 bitrate=6666.5kbits/s speed= 485x frame=41952 fps=11986 q=-1.0 size= 1375214kB time=00:27:58.00 bitrate=6713.8kbits/s speed= 479x frame=48039 fps=12009 q=-1.0 size= 1562378kB time=00:32:01.48 bitrate=6661.0kbits/s speed= 480x frame=54193 fps=12042 q=-1.0 size= 1754286kB time=00:36:07.64 bitrate=6629.8kbits/s speed= 482x frame=60008 fps=12001 q=-1.0 size= 1944828kB time=00:40:00.24 bitrate=6637.7kbits/s speed= 480x frame=60862 fps=12009 q=-1.0 Lsize= 1969864kB time=00:40:34.40 bitrate=6628.8kbits/s speed= 480x    
video:1827970kB audio:133124kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.447200%