Hi just saw this. I have a 2025 2500 6.6 L8T custom also, my truck makes the same noise you describe. Almost like a bad ground on a stereo through the speakers. I’ve had passengers ask if I had a turbo or supercharger. I only have 1400 miles and haven’t taken it in yet. I also have a bad vibration at around 4k rpm. Pretty annoying ! Did you get it figured out? Thanks in advance, Mike