Check MDI wires for the speakers if they are not broken. Also, it should be shielded wires for sound signal. And if you use 2 inline looms, i would cut one and solder to each other. Positive, ground, can high, can low. I had similar issue when added aux leads to MDI loom, thin wires got scratched/damaged during the fitting and making the noisy sound.
I have bluetooth, mdi, aux fitted, just no inline looms, everything soldered to the main quad lock.