Some light switches make a crackle noise when I turn them on and when I get close to them I smell a sulfur smell. I had an electrician change about 7 of them.. . but now on a few I still get that snapping noise. Should I be concerned?

If very loud from other maybe a bad batch, were exposed to salt air or corrosion?
Change the loud ones or all that was changed.
Should not be dangerous(In grounded box)should trip breaker.
If the crackling continues while light on, bad connections generate heat. Check to see if "Backwired", If so remove and tighten around screw.