Car Stereos: hissing noise on after market speakers, infinity kappa, defective line

Question
New aftermarket speakers Infinity Perfects in front and Infinity Kappa at the back with MTX TE 404 amplifier. I noticed some hissing noise from my speakers and the installer told me that it is the power of the amp thats making the "hissing noise" and can't do anything about it. It's just kinda frustrating because it sounds like listening to an FM station even though a CD is playing on my factory radio. Is there anything that i can do? Thanks a lot.

Answer
Assuming this is factory deck, the hissing is the noise floor of the amplifier usually resulting from incorrectly adjusted gain settings or a defective line level adaptor.
This issue can be resolved by reducing the gain on the amplifier to the minimum level, power up the stereo, set the deck volume at 3/4's and then slowly increase the gain on the amp until your volume is comfortable and clean. Then reduce the volume on your deck and listen to see if the hiss has been reduced. If it's still at an undesirable level, there may be an adjustment pot on the line level adaptor. If so, repeat the above process with the levels on the adaptor.  If there is no adjustment, you may have to look into buying a decent line level adaptor.