600C

I have recently purchased a 2023 Prado GXL, it has similar symptoms between 1400 and 1600 rpm the exhaust noise becomes a much louder droning noise. This is in 6th gear I assume . It is fine at lower or higher rpm . When accelerating up a hill or slight incline from 1500 rpm the droning sound becomes more obvious until the transmission drops down and revs increase then it disappears. I took it back to the dealer at 500km who said they had not heard of it before. They said it was noticeable, so they took another Prado for a drive, and it did the same thing. It wouldn't be so noticeable, but this rev range is what I find I use the most for my driving. I used the trans in S mode just lately so vehicle wouldn't change into top gear problem was gone so Iam guessing the higher gearing has something to do with it anyone else had this problem and had it rectified?