Electric "trills" at start up??

I recently purchased a 2017 Tundra with just over 100,000 miles on it. When I start the truck after it's been sitting for a few hours (i.e. overnight), the computer makes a series of high pitched "trills". Each time I start the truck, one "trill" is added to the series. None of the dash warning lights are on, the engine sounds normal, and the truck seems to be driving and performing normally. Haven't been able to find any information on what these sounds mean. Any insight would be greatly appreciated!