Maro claims that sonic attacks are mostly , but the only cards about that seem to be very old. Meanwhile, has gotten a few sonic attacks recently?

It's a bizarrely underexplored niche either way, considering how sonic attacks are common in various fantasy media.

Could be any color I'd think, depending on what the sound is doing. Blue has siren songs and stuff, white would have war drummers or whatever, green can get tribal drums and stuff, black gets I dunno, death metal maybe.

I feel like you could place melodic death metal into black/green actually.

I think the use of "echoes" often is metaphorical though rather than literally a sonic attack.

If you want to hurt something with the raw force of sound waves (Aka, a sonic attack) that does rather seem red. Other colors could utilize sound and sound effects in different ways (even red has other options) but as an attack element, it's red along with fire, ice/cold, lightning, and some earth. Outside of red you get traces of Earth in white and green, wood/plant in green, light in white, water (any state) in blue, and unspecified necrotic energy in black.

Music was represented in Urza's Saga in a double five-color cycle of enchantments that got verse counters:

http://gatherer.wizards.com/Pages/Search/Default.aspx?text=+%5Bverse%5D+%5Bcounter%5D

But that was long ago.

[makes a mental note to include verse counter cards in some portion of the Kyren Auction]

Black gets banshees.

gets the brown note.

Something as vague and broad as sound can easily be represented (and has been) in all five colors.

I love banshees.

Sound is pretty red. I remember a few cards in Onslaught block being red sonic based spells. A lot of Barbarian yells seems like a thing that make sense to me. War Cries, too.

I think attacks that have less to do with the actual sound and just the sound waves boggleing your brain is blue, but actual sounds doing harmfull **** seems more red to me.

Sounds rather intuitive. I'm guessing there's a lot of gray ground between the physical properties of sound and the more metaphysical ones when it comes down to its use.