Lightning sound

I have a problem where one mission uses the lightning with the thunder and strike sounds (works fine). I switch to another mission and when I fire the gun with no bullets (dryfire sound) I get the lightning crash sounds or sometimes when I run I get lightning sounds for footstep sounds.
The lightning I create on the fly in script and when mission is over I delete it. Seems to me the engine is not cleaning up the sounds on a delete from script.
I saw a thread about this some time ago and cant find it now. Anyone else see this happen or could point me to the thread?