One month ago i've started hearing a low interference noise while start my car and /or accelerate (WITH THE ENGINE COLD), as soon as I reaches normal temperature the noise disappears. Although my car is from 2003, i dont think it's normal. Also It's not a bad ground or something because i checked the ground of my battery, and my amplifier ground and both are very tightened. Also that noise is when i have my audio totally off. And also that very low noise comes from (i think) the engine NOT the speakers.
My sparkplugs are less than 2000 kilometers (about 1200 miles).
It definately sounds like an electrical problem to me. I don't see how the spark plugs could have anything to do with it, but are you driving a Ford by chance?
I am guessing that you have an aftermarket amplifier in your vehicle. Did you hook it up yourself?
the professionals should have grounded ur radio to the chasis of the car, not the vehicle wiring harness.. call back up there, and explain the problem, and ask them where they wired ur HU ground!
I had the same exact problem. when my brother wired my amp and subs. he wired everything on the same side of the car. he was supposed to wire the "hot" (power) and the audio cords on separate sides of the car. after i did that it went away.