I have a new 2022 signature with 8k miles on it. I've started to notice that it makes a faint whining sound at highway speeds, loudest around 65mph. If I put the car in Neutral then the sound goes away. When I put it back in gear the sound returns. It's not the turbo as that makes a different sound. Anyone experience this? Normal?
1st off, try not to do that again.
While it's not as bad as throwing it in reverse and dropping the tranny... A neutral drop & re-engage at highway speeds is causing additional wear and could cause some damage.
Modern powertrains are all computer controlled and interconnected. Engine, tranny, torque converter, gears, bands, differentials. Gears, teeth, fluid pressure, heat, etc. are all variables. All these affect and are affected by each other.
When you disengage the tranny to neutral at highway speed, the pump slows down, so now you have less fluid getting to the tranny and torque converter, etc.
Less lubrication, and less cooling of these parts. Also, pressure will be increasing. Less lube means more wear and tear. Ok, so you brake and slow down. All good.
But instead of braking and slowing down, now you re-engage. Now your dropping your tranny into gear at highway speed. Your dropping a huge amount of torque back into the tranny... Which is gonna put additional stress on the tranny, torque converter, etc...not to mention all the many moving parts and gears all trying to get synched together. You may even have felt a jolt or kick...that's your tranny telling you don't do that again.
While it probably didn't cause any major damage, it's still not good for your powertrain and most likely added some wear.
Now to your question. Low fluid comes to mind... But are you sure it's the transmission whining? Many different things could be causing the noise. It's under warranty. Just take it back and have the dealer look at it. If you are unsatisfied with dealer response(f.i. if they tell you nothing is wrong), then you can always take it to your local mechanic or take it to an AAMCO for diagnosis. AAMCO is really good...at least for me, it's always been a good experience.
Although there is general mistrust of dealers, there are some reputable ones. You should give them a chance to look at it then return here with any questions you may have about their diagnosis.
They will be able to look at & test the vehicle to help determine what may be wrong. Something that forum members can't do.
Other members can chime in with possible opinions but you really need to have a mechanic look at it.