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In my car these 2 noises occur. Though not consistently. At times, there's none.
A. Alternator whine
B. Slight krrrrrrrrrrr from the speakers.

B has been almost fully eliminated by grounding the HU RCAs to the HU casing. Do the amp RCA sockets also need similar grounding?

Why do these noises crop up? They were not there post initial install.

For alternator whine try relocating the RCA wires it helps a lot.

Current setup is this.
RCAs from HU, behind glove compartment along left side of car to Amp fixed to rear seat. Amp remote wire goes with the RCA in the same route.

Amp power cable runs under carpet along the centre of the car.

All speaker wires run along the right hand side of the car.

Amp ground wire is fixed to a screw on the boot. 1.5-2 ft length of grounding wire.

Now what new routes can I consider for the RCAs ? Also as I said, alternator whine is faint now, and intermittent.

Running speaker and RCA next to each other is not bad. It is the power cables that need to be as far away from the RCAs. Also good RCAs are shielded from this noise. and while ou are it if you have 2 or more amps keep in mind not to have ground loops.

Sorry for my ignorance,navinji

Please tell me whats ground loops ?

Lol! Apology accepted. But yeh, I think the guy messed it up. He's supposed to be one of the "better" installers in Bangalore. Will give the wiring and the grounds one more check, maybe elsewhere.

8 including 2 tweeters. I have a feeling the gains are high. Gonna go check the amps right after sending this reply! If that doesn't work, then wiring and grounds.

I'm playing mainly MP3. But the problem occurs in Audio CD format too.

It's just a steady hiss. There's absolutely no engine noise as far as I can tell (Maybe also because the hiss is so loud!!).

Yep! Exact same setup for my stuff.

@All : How much should a good wiring setup cost me. I've got whatever the guy put while setting my system up. Doubt it's very great quality. So if I must change my wiring, what should I go in for? Slight budget problems so I must start planning this much in advance :)

very simple...

say amp 1 is grounded at point A and amp 2 is grounded at point B and Point A and Point B are not the same there might be some minor potential difference between A and B and this will introduce a hum or hiss into the signal chain (music).

I am sure google can find better explanations. I'm not google expert but this is what I came up with

Noise Prevention
Crutchfield Tech Support: Noise Problem Troubleshooting: Popping noise
Car Audio Help Guide
Ground Q/A sticky

BTW I believe a Ground Loop Isolator is a band aid. if one uses some common sense it is quite easy to eliminate groud loops altogether.

thanks Navinji

those articles were very informative,helped clearing some doubts clap:

I know you might thing what differnce it will make. Just try this. Disconnect the remote wire and reroute it a little away from the RCA wires and tell us the result.

I think this is the best possible layman explanation of ground loops. This is more prone when multiple amps are used. But it can me there when HU and AMP grounds are not properly done.

I used to be a layman, atleast I'd like to think i was one. Today B&T, Sam and co have that title. :-)

"Just a gigolo, everywhere I go
people know the part, I'm playing
Paid for every dance, selling each romance
every night some heart, betraying"
- Bing Crosby

Now this is not layman terms, based on poetry.

Ahem, when DerAlte bhai said the ICE section was "singing paens" for me, I visualized it slightly differently. :)

Thanks. Will try this when I rewire in a few days time. I also need to check whether the RCAs are near the power wire, behind the dash.

Where is the HU grounded by default? Is there a grounding wire in the default wiring harness?

I was going through the first article @Navin posted. It seems the noise I have is due to the HU. Since with the HU on but RCA's disconnected at the HU end, there is no noise.

In the wire harness.

If this happens then the HU is not grounded properly.