Frequency of audio signals taken from multimeter
You are feeding hundreds or thousands of different frequencies into a device that is designed to display a single frequency.  What do you expect to happen?  At best the device will display just one of the many frequencies that are present in the music (and that number will be meaningless in the larger context).  At worse, you will confuse the thing and it will give you a completely bogus number.

If you used an o-scope and used the auto-measure feature to tell you what the frequency is then you would likely get an equally bogus measurement.  The only difference is that with an o-scope you could actually see that the number was bogus.

How do you know that the music does not contain frequencies in the 0-15 Hz range?  It is entirely possible!  Drums will often have some low-level noise in that range that is often not audible but is also not often filtered out of the final recording.  (Note for the pedantic:  frequencies under 10 Hz are often filtered out, but there could easily be stuff in the 10-15 Hz range).  I also recently worked with a recording studio that had equipment putting noise in the 0-5 Hz range into their recordings. 

Get an MP3 of a sine wave and redo your measurements using that, not music.  If the multimeter reports the correct frequency then my answer is correct.  If it reports some other frequency then the problem is something else.