For those who find this annoying. Open up DBM-core/dbm-core.lua
At line 2800 insert a new line with just the word "return" and it'll stop the sounds.
EDIT: the line in red is what you're adding.
if IsInInstance() then return end--Don't play joke if you're raiding.
DBM:Schedule(900 + math.random(0, 600) , DBM.AprilFools)
local x = math.random(1, #soundFiles)
if DBM.Options.UseMasterVolume then