Tornado siren sound during acceleration only

First thing I would check is the CVT - the Jatco CVTs are (kind of) known to fail due to intolerance of poor maintenance and lesser quality compared to the Aisin CVTs Toyota uses (which hold up a lot better because they have a starting gear, the Jatco doesn't). A lot of the failures are due to the weak nature of the early Jatcos (which is still a problem today, but they're not as bad as the earlier units), but some people put generic CVT or ATF trans fluid in them. NO CVT likes this; you need the OEM Nissan or Toyota fluid. You can put something like Amsoil fluid in a traditional transmission in place of OEM fluid, but CVTs do not tolerate it.

To quickly check for a bad trans, open the hood and listen in the engine bay. This is a FWD layout car, so the trans is transversely mounted to the engine. Have someone rev the car to 3-4krpm and try to pinpoint the noise, but focus on the CVT area first to rule out a bad trans quickly. It’s also not serviceable, so you have to put a new trans in, and it’s about as much as you probably paid for the whole vehicle. Parts and labor, even the parts, aren’t cheap for DIYers. You can’t even trust used ones because someone probably killed it the same way. And to add icing to the cake: Once it shows early warnings like weird noises, you're probably done for.

Now this shouldn't need to be said but I kind of have to but if you have long hair, use a hair tie and pin any flyaways with pins - you don't want to be face to face with an engine bay over long hair.

If the sound is coming from the middle and not anywhere near the CVT, it may be with the engine (CV joint, pulleys and belts), I would take the coils and plugs out and inspect them for damage or evidence of issues like oil consumption which will show up as black sludge on the plugs or cracked plugs. If that looks good, I would get a set of compact MEMS micrphones and place it on the trans, and a few places on the engine -- something like this: https://www.amazon.com/Steelman-06606-Ch...

You can probably get something cheaper, but check the reviews before you buy.