i have a loud noise in my speakers when i start my 2012 Lincoln MKZ

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! Well, that sounds like your Lincoln is trying to give you a very loud, unscheduled audio wake-up call every time you start it! The fact that the noise stops when you run the speaker self-test is a really interesting clue – it's like the system behaves itself when it knows it's being watched. You're definitely on the right track thinking about the Audio Control Module (ACM). The ACM is essentially the brain of your sound system. If it's got an internal hiccup, especially during its startup sequence, it could certainly send out some gnarly signals to the speakers. When you initiate the self-test, the ACM is forced to go through a specific diagnostic routine, which might temporarily bypass or reset whatever glitch is causing that initial blast of noise. So yes, a misbehaving ACM is a prime suspect when the self-test temporarily "fixes" the issue. While other things like an amplifier or even a quirky ground could sometimes cause noise, the self-test behavior points more strongly towards the control unit. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554