I wanna share my experience to everybody recently hoping this called help my fellow iStoryans.
Before my ride was sent to the shop for tune-up, HER audio setup works perfectly (meaning no distortion).
When it's time to fetch my ride I noticed a whistling sound on my separates when i accelerate.
I search the internet for same issues regarding their sound setup.
For 2 hours of research, someone advice me to check the a ground if it taps to the transmissions body.
So this morning I immediately check the grounds and exactly there are 2 grounds now connecting to the transmission's body.
I transfered the grounds to another part of the engine block and drove my ride to test. Indeed it solve my problem! There's no more distortion (whistling noise) from my separates.