capacitor as a noise filter?

Hey guys, Ive been going through insane amounts of noise problems with my car in the last few months.  I figured out recently that my amp is not shot like I thought it was, but somewhere along the line Im getting noises that randomly started one day.  I am going to get a ground filter from david navone, but I would still like to provide some form of filtering for my + (amp input).  Ive heard a few times on here that you can use a cap as a noise filter for your power wire, seems like a pretty good cost effective solution.  I would never use a cap for any power surge purposes, already have a 200a alt, and two yellow tops, along with 0/1awg big three, car has no trouble powering my two amps (hell it could probably power a small city at this point).  I just wanted to make sure that caps are at least somewhat helpful in use as a power filter, and possibly a small explanation of how/why they function as a filter would be nice if anybody knows.

Thanks,

Jeff

A good definition of a ground loop (from http://www.epanorama.net/documents/groundloop/basics.html):

A ground loop occurs when there is more than one ground connection path between two pieces of equipment. The duplicate ground paths form the equivalent of a loop antenna which very efficiently picks up interference currents. Lead resistance transforms these currents into voltage fluctuations. As a consequence of ground-loop induced voltages, the ground reference in the system is no longer a stable potential, so signals ride on the noise. The noise becomes part of the program signal.

My bet is,  you find the source of the noise by doing a thorough examination of the grounding.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Start with the connections that are presently there.  You stated, "but somewhere along the line Im getting noises that randomly started one day."  Something changed, broke, or corroded to the point that this change occurred.  It didn't go from silent to noisy without a reason.  And also think back to when this started and figure out if YOU made any changes at all to the car or to the system at about that time.

You know when you use a soldering gun, after some time and use you have to loosen the nuts that hold the tip in place and then retighten them.  After you do that you get full power again.  Sometimes you have to sand the tip in the process.  There is a buildup of oxidation that occurs on that iron and the electrical connection is adversely affected.  By cleaning it up and re-sanding, you allow full electrical flow again.  Same thing with the connections of wiring in your car.  This may not be the answer, but it's the first step in looking for it.

As far as the stiffening cap goes, it should smooth the ripple a little but it won't have anything to do with noise.  You don't need one with our modern amps, but it might give you a psychological advantage....

Yeah that is my biggest confusion with all of this and what really makes it so frustrating, I was finally at a point where I hadnt touched my setup in like 3 months where I normally tear mess with it one way or another on a weekly basis (mostly just for the sake of playing with my own stereo instead of a customer's for once).  So no real changes had occured and it just sorta happened one day.  I will start really checking through all connections, Ill borrow two ground loop isolaters from a friend and plug them in to see if they help.  Hopefully this wont be as painful to fix as it has been seeming thus far.

As far as the psychologic advantage of having a cap to cleanse my power line, at this point I would almost consider that worth it haha.  Its times like these I ask myself why I got into this hobby in the first place, but I still have to love it.