SLI can reduce/solve coil whine?

No SLI wont stop it. Is it when under load such as gaming? If so cap your frames to your monitor refresh rate.

margrave55 said:

Coil whine?

When under load, components works harder and can vibrate emitting sound

PolarNettles said:

When do you get the coil whine? Is it at high FPS?

I would look at your power supply first to make sure it's capable of handling high peak currents on the 12V rail. My 1070 whined horribly until I replaced my old Antec 650W PSU with a modern EVGA 650W PSU.

Very true on PSUs, good advice

If anything, having 2 gpu's will only increase the coil whine as you'll have higher temps.

Good suggestions here. PSUs can mitigate coil whine if it's running on a good quality rail, but coil vibrations are normal if you're trying to push the card(s) power constantly, good example being unlimited rate of displayed frames. it's also not dangerous, and can even fix itself during heavy load. It's mostly just annoying to the ear. SLI won't do much if you already have issues with coil whine. You need to either replace the card under RMA (which few manufacturers do because inherently there's nothing wrong with the card), or you could try your luck with a new high tier PSU which may or may not alleviate it.