[Wayne D]

Thanks for the advice guys.
I've used a Scosche Wiring Kit so i think the cables are of good quality.
Yes even when the volume is it one or even when the system is off there is a very slight constant noise which doesnt not change with acceleration nor has any effect on the sound of the ignition of the car. Its better than before though but i would still like to get rid of that sound if possible.
Yes the wiring has been run on opposite sides of the car wiith the RCA cables on one side and the power cables and speaker cables on the other.

[rohitabc]

Same problem i am facing from last one year..

The sound really sucks maan

[DerAlte]

Originally Posted by omishra

... Also some how tune Amp input so that it senses anything above 100mV of signal. I mean reduce signal from input cable to 1/5 using attanuator [Guru's please advice] before it enters Amp and then increase to accepted levels. ...

Mishra-ji, that would be like adding sugar to a dish to compensate for too many chillies! One will land up with a hole in the signal, effectively removing most of the nuances in the music. A palliative will not cure - for that good cabling practice and some tricks, like putting a high voltage cap across the alternators DC output, are indispensable.

[omishra]

Originally Posted by Wayne D

Yes even when the volume is it one or even when the system is off there is a very slight constant noise which doesnt not change with acceleration nor has any effect on the sound of the ignition of the car.

This is stationary noise and it will remain there. No need to run after it. SX4 HU has better S/N after level 15 of volume control. Below that you have hiss, irrespective of music. and muting HU does not mute AMP, hence you still able to listen noise. That's why I used mute logic to mute my amp.

Originally Posted by Wayne D

Its better than before though but i would still like to get rid of that sound if possible.

Originally Posted by DerAlte

Mishra-ji, that would be like adding sugar to a dish to compensate for too many chillies! One will land up with a hole in the signal, effectively removing most of the nuances in the music. A palliative will not cure - for that good cabling practice and some tricks, like putting a high voltage cap across the alternators DC output, are indispensable.

Sir ji - greetings! I agree. Along with noise you are dropping audio too but that lost signal can be regained after increasing volume a little bit while noise can not be.

I stopped saying that "you can add 10uF,35V Tantalum Cap across power lines inside HU and AMP."
This in my experience solves noise from power lines but somebody rarely dares to do this. [Somewhere it is related to battery impedance and/or its age. Here I assume "exide".]
IMO, first place to be looked in wires, layout and shielding.

[navin]

Originally Posted by DerAlte

A palliative will not cure - for that good cabling practice and some tricks, like putting a high voltage cap across the alternators DC output, are indispensable.

or get a better alternator.

Originally Posted by omishra

This is stationary noise and it will remain there. That's why I used mute logic to mute my amp.
I stopped saying that "you can add 10uF,35V Tantalum Cap across power lines inside HU and AMP."
This in my experience solves noise from power lines but somebody rarely dares to do this.

I am a bit surpsied that modern cars still face these issues. My mom's NHC, Wife's Opel Sail nor my Octavia had an issue.

Is this a problem of poor parts of poor wiring?

If this noise is entering the circuit through the sehild you can try covering the RCA wires in aluminum wrap.

[omishra]

Originally Posted by navin

or get a better alternator.

I am a bit surpsied that modern cars still face these issues. My mom's NHC, Wife's Opel Sail nor my Octavia had an issue.

Sir, You did not mention Maruti

Originally Posted by navin

Is this a problem of poor parts of poor wiring?

If this noise is entering the circuit through the sehild you can try covering the RCA wires in aluminum wrap.

SX4 HU sucks, whatever you add to get better sound, improvements are achieved. Still its inbuilt capabilities and quality can not be raised beyond certain limits. Just like constructing a huge building over a weak base. [I restrained myself putting more money after this, except - add enough power <20W RMS/ch , good Components and damping]

[navin]

Originally Posted by omishra

Sir, You did not mention Maruti

Is this a problem only with Marutis?

[omishra]

Originally Posted by navin

Is this a problem only with Marutis?

Not sure with other maruti cars!
But I assumed that SX4 is premium car from maruti. I confirm that its HU has in built hiss and little engine whine present.