I just got done installing my system in my truck today. Everything works great with the exception of one thing. When I turn on my truck before my head unit kicks on there is a very loud pop in all my speakers. Once my head unit starts playing music everything is fine. It's just the one loud audible pop that happens after I turn on my truck and before my head unit kicks on. Is there any advice you can give me to get rid of this or let me know that it is normal. Thank you in advance.

 

Relay Pop
Relay turn-off pop is caused by components in the system turning off before the amplifier completely shuts off. In most cases, the component will be an EQ or signal processor. Usually adding a little turn-off delay to the offending processor can fix the problem. This allows the processor to turn off after the amplifier, preventing the pop. Many components have this feature built in, and it is adjustable. Check the manual to see if your component has this feature available. If not, you can build your own delay circuit with a diode and a capacitor. Add a 1N4004 diode in series with the processor's turn-on lead, striped side toward the unit. Then add a capacitor in parallel, the positive side of the cap connected to the striped side of the diode, the negative side of the cap to car chassis ground (not to the body of the radio or processor chassis). Experimenting with the capacitor value will give you just the right amount of delay before the EQ shuts off. You don't want the delay very long, just long enough to make sure the amp is off before the EQ powers down. Usually 220 - 1000uF is about right. Make sure that the cap is a polarized electrolytic, 16V or higher.

 

Ground Loops

When any accessory uses the body of the car for ground, other accessories that use the car body for ground can form a common return path. In these cases, some accessories can limit the amount of ground that other accessories can receive. This is commonly known as a ground loop. If the amount of ground return is affected, then the amount of power into the component is affected. In autosound components, this can greatly affect the amount of power output, as well as cause noise.
The best place to establish a common Signal Ground is at the back of the head unit. Since the head unit has to be at one end of the system, and the amp is at the other end, it is a great place to establish the one-and-only signal ground. This is normally provided by all modern head units, which use the same reference to ground for both left and right RCA shields. The main goal is to make sure that this ground is allowed to float all the way to the amp(s), and not get misdirected along the way. The same signal ground seen at the deck must carry down through the rest of the components to the amplifier. If the grounds are different between any two components, ground loop noise can creep into the system. Most autosound components use a single signal ground by floating the component's signal ground and allowing all grounds to reference back to the head unit. Sometimes, though, the signal output ground will be chassis-grounded on an individual component. If that component does not use DC-to-DC converters in it's power supply to isolate that ground, their signal outputs will be grounded, and noisy. It may be preferable to substitute a more expensive component (with no chassis ground on it's output) than spend hours trying to trace the whine. If there are several suspect components in line between the head unit and the amp, just take a long RCA cable and run it straight down the middle of the car (over the carpet, seats, etc.) straight to the amp. If the noise goes away, then it's time to check each individual component. One method of finding out which component is responsible is to bypass one component at a time using double female RCA barrel connectors. The barrel connector will float the outer shield of the RCA, preventing a second reference ground and a ground loop. If the noise goes away when you bypass a particular component, then you have found the culprit.
As for Power Supply Grounds, it would be a good idea to have all of the components grounded to the same spot as well. For this, the best spot is at the amp location. The amp will normally need the most power of any component in the system,, therefore it's ground cable needs to be the shortest (in order to have the least resistance). For the head unit itself, you would want to make sure that it is not grounded anywhere up in the front of the vehicle. Instead, you would want to extend the unit's ground wire (using the same size wire as what comes on the unit's harness)all of the way to the amp location, and ground it to the exact same point that the amp is grounded. The reason for this (as with Signal Ground loops), is that if there is any difference in ground potential between any of the components in the system, it can cause a ground loop and draw noise in over the power supply. All powered accessories need a ground to work properly. If these components are trying to use the same ground path through the body of the car, then this can cause ground loss in any other component that is hooked up to the same ground path. When this happens, the unit does not work as efficiently, and in the case of autosound systems, can cause noise as well. (This is one explanation for why a car's headlights may dim on deep bass hits; because the headlights and the amplifier that is running the subs are on the same ground path. It can also be because the sub amp is pulling so hard on the alternator that it can't supply enough current to run other accessories properly.)