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How long has the whistle noise been happening? Are you positive it's from the transmission?
How long has it been since the trans fluid/filter have been replaced?
There is definitely going to be some solenoid buzz when you put it in gear. The new solenoid packs are quieter than the older ones, but there is still some noise. That's nothing to worry about.
A noise that comes from the trans when it's in gear generally comes from the torque converter. The first thing I would recommend is trying to pinpoint whether the noise is actually from the trans. If it is then the first thing I would recommend is dropping the trans pan and replacing the fluid and filter. A split, cracked, or plugged trans filter can cause the pump to starve for proper fluid flow and cause noises like this. The mileage interval in the owner's and service manual for transmission service on your car is every 60,000 miles or less, but every 30,000 miles is recommended, especially in stop and go use. If replacing the filter doesn't take care of the noise and it's definitely coming from the trans then the torque converter may be failing.