noise from tweeters with car running

Hello all, I am pretty new, and I have been reading the forums for a while now, and I have to say I am much more knowledgeable since reading this. Anyhow, onto my question. I own a 1997 nissan sentra, and have recently installed: 4 crunch gtr components, 1 crunch pzi 175.4 amp, 2 mb-quartz speakers, and a kenwood kdc-mp635 deck. With the engine off and it on ACC I get crystal clear sound. But as soon as I turn on the car I get a weird clicking sound out of just the tweeters. In order to try and diagnose the issue this is what i have done. I have pulled the RCAs out at the amp and it is crystal clear. I pull the RCAs out at the head unit and it is still crystal clear. I then plug the rca's back into the head unit and unplug the antennae and still have the clicking sound. Also the clicking does not change with speed. I have changed the ground of the head unit and it still is the same. Thank you for all the help and these forums are awesome! Thanks all!

Your components are powered from your head unit, not the amp I assume, since you say things are "crystal clear" if you unplug the RCAs to your amp?  So I assume the amp is powering a subwoofer, not the mains?  If that's true it sounds like you probably have a ground loop (bad ground on the amp) that is affecting the HU and it is not built well enough to keep the noise out of its amplifier circuit.  OR you may have installed the crossovers for your components in a bad location and they are picking up noise that is somehow related tot he subwoofer amp.  In any case, check your amp ground return resistance first and improve the ground if it's above one ohm and see if that helps.

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Hey, thank you for helping me with this, by clear I mean that there is no clicking sound. I have not yet installed a subwoofer, and this amp is for the components, and there are no speakers directly hooked up to the headunit. so when I unplug the RCAs from the headunit or from the amp, I don't hear any clicking, but as soon as I plug into the headunit, the clicking begins. Sorry for the confusion, ha ha. Thank you for the quick response!

If you unplug the RCAs then the amp is not receiving a signal, right?  The speakers go dead, right?  OK, so I still suggest you verify your amplifier ground and you might also try using a different set of RCA cables.  If the ground is good and different cables don't help, then it is either an installation issue with the location of the crossovers or some other component (or a loose speaker wire) or a defective HU or amp.  Good luck!

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Hey, thanks for responding, I have a 4 gauge wire running from the battery to underneath the drivers seat in the car. The head unit is plugged into the factory harness except for the ground which is attached to the mounting bolt for the center console. The patch cords run near some wiring along side the car which could be for the fuel pump but I am not sure if that is what they are.

In the event that the problem disappears when the RCA’s are disconnected then the problem is not your passive crossover location.
Your problem is one of two.
1.     Ground potential difference between you head unit and amp.
2.     Inducted noise along the signal path (RCA’s).
What I do is take a 10 gauge or larger wire and temporarily connect it from your amps negative terminal to your head units chassis. By doing this you are ensuring that the ground potential difference between the two are nearly eliminated.
Listen for the noise at a volume level of 2 or 3.
In the event that the problem is not effected, you have a radiated noise problem and not a ground issue.
If the problem disappears then fix your ground. Check both your amp as well as your deck. Are you using the decks factory ground???? Shame on you! Go to the kick panel.
If the problem is helped but not eliminated then you might have a combination problem of ground and radiated.
If you determine that you have a radiated noise problem then first check your gains on your amp. Are they as low as they can possibly be yet allow you to achieve good volume? They should be.
Next suspect that your deck might not be producing enough preamp voltage to overcome radiated noise along the RCA’s.
You can attempt to physically move your RCA’s. Run them on the opposite side or tuck them farther under the carpet. But ultimately if you are experiencing noise problems do to low voltage at the RCA’s the solution is to boost that voltage to a level that will kill your noise problems and at the same time improve your amplifiers dynamic range performance.

\Let me know what you find. I am curious.

Hey all thanks so much for replying! ok so in regards to your question I am an idiot- the clicking occurs every second if not more often. Speakermakers-when you say amp's negative terminal do you actually mean the ground? and when you say to the head units chassis you mean on the external of the head unit not to the ground wire, oh and no I did not use the factory ground haha. Thanks again all!