It's a simple fix really - not targetable on base sector. Other arty's already do this, just add this to the list. Fixed.
Only arty that is not targeted on a single point (but a sector) has this property AFAIK. Scavenge artillery does not operate on a sector like sector or assault artillery do. What you're proposing is essentially losing the ability to call in this arty on a specific location like most other arty callins work.
Do you have separate output devices (headphones and speakers) visible in the Sound app in Control Panel?
If so, you could try setting headphones as the default device since CoH 2 probably just goes to the default device as it provides no option to select a specific one.
I'm experiencing this as well on a GTX 670 when otherwise I can get solid framerates. No matter which drivers I use the performance hit is big with smoke and incendiary flame, especially if you zoom in on it.
It might be an nVidia card issue with the CoH 2 engine (which supposedly likes AMD more) or it could be just the fact that the smoke effect requires much more GPU power than the usual, other stuff displayed. It looks to me like the engine actually uses many transparent layers to produce a single smoke round. Add several from a plane smoke drop or assault artillery and it all stacks up.