New to the forum and need help. 2008 CTS Luxury (Mid) model, 3.6 w/ 150K miles, bought a year ago w/ 137K. There is an electronic series of tones that are inside the passenger compartment when driving, low speed to 40mph. Diminishes in tone and volume when slowing. It sounds like whale songs. Seriously! It starts with a faint, lower tone, then slightly higher tone, then another different tone. Each lasts a few seconds. Never more than one tone at a time (no overlap). No bluetooth, OnStar not activated, no weight or electronics sitting in passenger seat. Does not seem to be mechanical, but have replaced hub bearings (ABS rings fell apart). Replaced carrier bearing (rubber rotted). Tires rotated and balanced with good M&S tread. Not road noise. Definately electronic. Does not seem to have a louder area or direction in interior. Retired ASE Master Tech for 40 years but this has me stumped. Wife's car and she adds a her own high-pitched "whine" noise with her unhappiness about the noise!