Okay just some general brake stuff. You don’t tell us what kind of bike or brakes you have. Some pads just have to wear in to lose the sound problem. You do need to make sure that the pad does not touch the rim all at once. One old trick is to put a wire tie on the back end of the pad and set the pad to touch the rim with the front edge of the pad and at the wire tie. That will give your pads an angle and that angle will keep the 18 wheeler sound from happening because the pad doesn’t grab the whole rim at once. Instead it is a progressive pressure that builds as you add pressure. You might also need to clean the rims. Aluminum can hold a lot of dirt and rubber and you could have build up of rubber and gunk that is adding to the sound.
Cheers