Just this AM I noticed a whining sound in my 2015 Optima …that goes up or down with the car speed…it is especially noticable when slowing.
If you are still in the warranty period use it.
Let us know if the whining changes pitch with the engine in neutral and you rev the engine a bit.
Yosemite
There’s a wear gadget in the brakes that could cause this. It’s to tell the owner the brakes need the pads replaced.
Turn the radio off. Noise gone? You might have a bad radio ground, and if that doesn’t solve it, a ground loop isolator will.
If the noise is still there with the radio off, I’d be looking at the alternator first, and anything else with a pulley second.
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No the rpm’s of the engine, has no effect…Although I found that this whine only occurs when driving with the transmission mode selector in the "normal shift mode’… it is silent with no whine …in the “economy shift mode”… The manual says some models have a third “sport mode” but my not mine.
I had my mechanic drive it and look it over…He says he cannot identify the source… Probably the dealer is the only one who may have heard of this problem…
Does you car have a CVT-type of automatic transmission? Those can be more noisy than the conventional automatic. From the link below:
Rubber continuously variable transmission (CVT) belts are extensively applied in automotive industry. The tones of belt ‘whistle’ noise, which vary with belt transmission speed during low- and high-ratio operations, annoy drivers, especially when the throttle is closed and the vehicle is in motoring condition.
I’m not sure any manufacturer still using rubber CVT belts, seems metal belts are used nowadays and it is no noise really.
…except when they aren’t…
Subaru utilizes a very stout roller chain in their CVTs, which might explain why their CVTs are more reliable than the CVTs from some other manufacturers–particularly…NISSAN.
Automobiles use metal belts in CVT transmissions.
This is the next sentence in that link;
In this study, two types of scooters with different cylinder volumes are taken as examples to cope with this problem for reducing belt noise.
Nissan… I happen to own few of these 
The trouble with them is not a material of the CVT belt (it is also all-metal), but something else.
Prior generation of their CVTs (using NS-2 fluid) seem to be working more or less OK from what one fellow told me at dealership, while last gen with NS-3 fuid was a disaster.
I’m taking it with a grain of salt, but two prior-gen Altimas work reliably for me and my daugter, 78K miles and 96K miles now, while my wife’s car with last-gen CVT failed at 42K miles with clanking and chattering sounds, CVT was replaced under warranty, I disposed this car as soon as I could find somebody paying a good price for almost new looking vehiucle at private party.