This is what I am doing in my profile, before targeting:
Code:
TargetFrame:SetScript("OnEvent", nil)
ComboFrame:SetScript("OnEvent", nil)
After:
Code:
TargetFrame:SetScript("OnEvent", TargetFrame_OnEvent)
ComboFrame:SetScript("OnEvent", ComboFrame_OnEvent)
This should negate the sounds and some other issues that can occur like target/combo point frames or target buffs/debuffs flickering, it is also slightly more efficient because it prevents the Blizzard UI running its own code on PLAYER_TARGET_CHANGED events.