Hi guys! I was hoping someone could help me with this issue. I have tried everything I could think of and am becoming extremely frustrated with this issue. I am a new audio installer, so if I didn't think of something, please let me know.
I have a 2007 Mazda3 that originally had the BOSE system installed, but I decided to upgrade to components that I had from a previous install. The amp is an Alpine which is 85W X 4 channels, and four new 6X8 Alpine speakers. I basically created an adapter which taps the BOSE high level signal and converts them into regular RCAs for my amp. I did this because I wanted to keep the stock head unit, and I wanted my LCD screen above it to function as normal.
Everything is working fine, except I get this high frequency white noise (hiss). The noise is audible even with the gain all the way down and the volume about 2/3 up. As the gain is turned up, the noise becomes much louder. As I turn the volume up, the noise becomes louder as well. If I turn the head unit off (And leave the amp on), the noise goes completely away.
These things had NO effect on the noise:
Unplugging and pulling back the antenna
Unplugging and pulling back the CANBUS (For the LED Display over the Head Unit)
Pulling the entire radio out of it's home with the antenna and CANBUS unplugged
Turning on the car, or revving the engine
Rigging up a different head unit and plugging in a set of regular RCAs
Using a different brand of RCA wire, and splicing it to the harness without it being run under the car
This DID clear up the noise issue:
Plugging in a separate set of RCAs directly into the amp, and then into my IPOD/Phone. I also turned the IPOD to max volume and gain on the amp all the way up; no noise at all. When doing this, I was bypassing the RCA signal to be sent to the amp, but I was NOT bypassing the speaker-output portion of the harness (IE the factory car speaker wiring which I also made in the adapter).
I checked my harness, and everything as in and all the pins were in the correct order. The ends of the adapter and RCA wire were soldered correctly. I checked the amplifier ground, and it seems to be fine. I am using 4 GA wire to ground it. I have no idea how to ground my head unit other than how it was grounded when it came with the car, but I did try to take an 8 GA ground wire and touch it to a metal part of the car. I also tried taking one part of the RCA and grounding it to the chassis. These attempts did not help anything.
This issue is really confusing to me. I don't know the source, or even what else to do in diagnosing the problem. This amp worked fine in a 1995 Sentra with stock speaker wiring. I can only guess it has something to do with something behind the head unit because a separate unit with different RCAs produced the same problem. But I am still not sure as it correlates to nothing else. I looked all over the web and nothing has a definitive answer on what type of interference would cause "white noise" or "hiss". Would a bad ground cause hiss? What about components radiating EMF? What can I do to find out what the issue is, and how to fix it?!?! Help!!!
