you need a noise surpressor. It connects inline on the posotive or ground (I'm not sure). I need one in my truck as well, it is caused by altenator whine. This doesn't mean that the altenator is bad. Make sure that you get a good quality supressor.

 

Yeah that should probably do the trick. Sounds like you are just getting noise in the power wires (especially since it only happens when the truck is running).

 

I have a similar problem. I get a buzz/static on the stock radio but not when playing a cd. It's worse on the lower end than the higher end of the stations. Outdoor temps affect it too. Some days when warmer it doesn't do it as bad and sometimes worse on cooler days. It only does it when the engine is running. I added a noise suppressor on the positive side feed and not the memory feed of the radio. Made no difference. I've checked the antenna and all is tight. I prefer keeping the stock radio even if I have to get another one.

2002 ZR2 Blazer

 

It could be a loose connection in the antenna that is plugged into the back of your factory head unit.

As previously stated, it could also be your alternator or the head unit itself. I would try playing with the antenna system AGAIN (since it doesn't cost anything) and rule out a poor connection.

I accidentally ripped mine out of the back of my head unit when I had the dash apart and all it would pick up was static. I just super glued it back into place.