Hi, GiaJoe -
Another solution that some folk use is a dummy jack in the headphone or external speaker port. Plugging a jack into that port will kill the internal speaker sound - so all that is needed is an unwired jack. Insert it before booting, and all sound will be eliminated.
Since the sound out port is on the back of your machine, a software solution would usually be more comvenient.
However, if you have external speakers which have their own volume control, you can use that to lower the sound during boot.