Subwoofers make a loud noise when tunining on the car

[is200bcs]

Hi lexus people, ok so i have just installed car subwoofer in my daily driver is200 and its sounds ace really good sq from a JL audio 12. Now what the question today is that everytime i turn on and off the engine, its makes a thump noise on full volume and the kids are getting scared lol, even when its on a low volume which is not good. Had a look on this car audio install system website that i have found online and its says its because the radio is coming on quicker than the actual amp, so do i need a relay? Which one and could i also build one?

[Neil E]

Firstly I commend you on the choice of sub but be careful about using full volume, JL make a point of warning their customer that these products are capable of sound levels that can damage hearing. 

What make of head unit and amplifier do you have?

Have you checked that all of the connections are secure and in particular the blue remote lead that runs from the head unit to the amplifier?

[Geoffers]

It's usually the amp turning on before the radio so picking up the crap the headunit generates as it powers up.

Does your amp switch on using the blue control as Neil says? If you are just powering on and have your control (not power) directly to iginition then instead you'll need to connect it to the headunit control or, as you say put a delay onto the power on. You can throw together a delayed relay swtich on but just need a little more circuitry for the delay. This circuit will give about 3 secs delay.