Buzzing noise, but not all the time.

I also posted this in another forum, sorry for the double post.

I finished my stereo last week.

Sony Xplod CDX-MP70 MP3 Player

Here is the problem:

There is a noticeable buzzing noise that comes on only once in a while, when it wants to, there is really no set pattern.  If I shut the deck off, turn it back on, the noise usually goes away and then comes back in a few min.  You usually hear it when you turn the volume all the way down.  When the buzzing noise comes on, you can hear it fade in, starts off low, then gets louder.  The funny thing is, if you turn the volume up just one click, the noise gets quieter, but is still present.  I believe this is not any type of power or ground problem because of the following, the noise does not get louder when you step on the gas, and the noise can happen with the car off.  Patch cables were run on the opposite side of the car away from the power cable.

Anyone have suggestions on this one?

Thanks

Thanks for the reply.

If it was alternator noise, wouldnt it get louder when you step on the gas?  It also does this with the car off as well.