Whistle Noise in 4th 5th and 6th

[Gustavo Toscano]

Hello guys, I bought this car last summer and it came already with this sound, I’m not expert in cars and thought that was a normal sound. The car have some mods, custom exhaust, custom intake, silicone tubes and I think the car have a repro. This sound only starts when I’m in 4.ª,5.ª and 6.ª and when I'm the pressing gas paddle and there is no problem when I switch gears. I think this may be a transmission problem but IDK. Any ideia?

Here you have a video showing the problem: https://www.youtube.com/shorts/JFsNi-42kw0