The use of a musical piece from Internet, as from any other place, is not possible without first having gotten the authorisation of those claiming their rights. Really the SIAE is the only body where one can turn to as the situation could become very complex according to the type of song one wants to use, as there are different rights depending on the songs. First of all, there is the right of the author of the piece and, eventually, the lyrics; royalty is due to the author for the primary copyright and also his authorisation needs to be asked.
If the author is Italian, you need to go to the SIAE for the authorisation as this body acts as an exclusive go-between of the rights and takes care of sharing the royalties to the concerning parties; but if the author is foreigner, then it is necessary to go directly to him, or the foreign body taking care of collecting the royalties on his behalf.
To these primary rights you must add the secondary rights, due to the company who recorded the song and likely translators or executors. The collection of these royalties is given, in Italy, to the SFC of Milan who has made an agreement with all the main companies for gathering together the royalties on their behalf; but even in this case if the recording company is small and is no part of an agreement made with the SFC, then you need to go directly to the recording company and negotiate the amount of royalty and the method of payment directly.
It is not always an easy to follow procedure and, unfortunately, the matter does not change if only a few seconds are used, instead of the whole piece. Obviously, in the case where only the music has been reproduced, maybe playing it on your own, it would not be necessary to pay royalty to the producer or the translator, but it would be nevertheless due to the SIAE for the author’s rights.