Silent Song

The Midrash (6:10) says תָּנֵי (במדבר ז, ט): וְלִבְנֵי קְהָת לֹא נָתָן כִּי עֲבֹדַת הַקֹּדֶשׁ עֲלֵיהֶם בַּכָּתֵף יִשָֹּׂאוּ, מִמַּשְׁמַע שֶׁנֶּאֱמַר בַּכָּתֵף, אֵינִי יוֹדֵעַ שֶׁיִּשָֹּׂאוּ, מַה תַּלְמוּד לוֹמַר יִשָֹּׂאוּ, אֵין יִשָֹּׂאוּ אֶלָּא לְשׁוֹן שִׁירָה, וְכֵן הוּא אוֹמֵר: שְׂאוּ זִמְרָה וּתְנוּ תֹף וגו', וְאוֹמֵר: יִשְׂאוּ קוֹלָם יָרֹנּוּ.  How can the Midrash interpret the word ישאו to mean song if it says בכתף ישאו, what does singing have to do with the shoulder?  And why does the tense in the possuk switch from plural, עליהם to singular, בכתף ישאו and not בכתפיים?  The Emrei Emes says the intent of the Midrash is not to say the לוים actually open their mouths to sing song but rather that the act of carrying itself was a song.  When the Leviem appreciated how their avodah was an act of service to Hashem, their limbs sang songs.  It is when one knows Hashem is with him in his actions that one's actions become praise for Hashem.  When that is joined with one cohesive group acting as a single individual, בכתף, then it becomes a symphony of various instruments combing to give praise.  It is the silent, united song that forms the greatest composition.