In a 2003 Vibe with factory Moon & Tunes, factory speakers, and factory aux amp, the white-noise hiss is ALWAYS present when the head unit is on.
It's less noticeable with the engine running, and when the system is playing radio, CD, or music, but it is always there.
Turn off the factory head unit, and the factory aux amp under the front passenger seat continues to emit an audible white-noise hiss through the speakers for about 20 seconds before the aux amp powers down, even with the car switched off.
So, as I recall, one of the reasons the line output converter was created for this setup was that the factory speakers were rated at just 2 ohms.
The other reason being that there was no line-level outputs on the factory head unit, nor the aux amp.
Owners who replaced the factory speakers with 4 ohm or 8 ohm units without changing the head unit and amp also noticed a significant loss in volume.
Why? On the Vibe new car spec sheet, a Moon & Tunes with "6 speakers and a 160 watt amp" into 2 ohm speakers looks far more impressive than an "80 watt amp" into 4 ohm speakers, or a "40 watt amp" into 8 ohm speakers.
The factory subwoofer was first available at the start of the 2005 model year ("smooth nose"), available at dealers as early as May 2004.
My 2003 Vibe Base Auto 2-tone Salsa "SalsaWagon" was built in May 2002. I acquired it in Feb 2004/Traded it in on a 2016 Honda HR-V in Feb 2018
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