The noisiest mantra practice I have ever done? Nam Myoho Renge Kyo at a Nichiren meet being played loudly in a soundproofed basement. As it was my first visit, my appointed guide was amazed I sat through an hour and a half of this buddha bombardment …
As we refine our quietening:
Each of these have benefits and possibilities. So for example Vajrayana/Mantrayana will accompany mantra with bells, drums, conch shells and instruments made from human bones to scare away demons. Ay caramba!
Moving towards the softening of the mantra requires a more developed focus/concentration.
Silent mantra recitation is more prone to wander away if not stilled.
Anyways that is my experience. What is yours?