Once you have about 300 minecarts stacked inside each other the sound engine will just give up and not play any sounds. This is in spite of the fact that the minecarts aren't actually producing any sound. This affects a very big area away from the minecarts.

Steps to reproduce:

1. Summon 300 minecarts with a command block (they must be placed on rails)
2. Do any action which would produce a sound

Observed result:
No sounds play: sound_suppression.mp4

Expected result:
Sounds would play.