I have a 1989 GMC Sierra 1500. Whenever I turn on my radio while the vehicle is cranked, this really annoying static hissing sound is there. It gets louder when I accelerate and the automatic transmission changes gears. Does anyone have any idea what this could be? Thank you.

Usually this happens when you have a bad ground somewhere in the radio wiring. Try checking the main radio grounds, and also the larger ground strap that connects the back of the engine block to the firewall by the heater core drain hole. If that doesnt help, go to Radio Shack and pick up an inline RF filter and install it on the main power cable to the radio. One or both of these tips should kill the noise. If it doesn't you may even have a bad radio module (the computer looking silver box under the middle of the dashboard). They are known to fail in these trucks due to rainwater from the antenna leaking down into the unit. Be sure to let us know what fixes it for you. Good luck!

Not to hijack this post but would this fix also work for a CB? I have tried grounding the CB to the frame, firewall and battery and still get a lot of interferance when I am on the freeway. Do the Radioshack things work well for CB's.

All those filters are for the most part are capacitors in the micro farad range in a pretty shell and wires.

For CB's, it won't necessarily stop the noise but it will filter some of it out. Same with the radio.

Aside from checking all of the above, make sure to check your spark plugs and spark plug wires to make sure they meet specs for filtering out noise. I can't remember if the resistant or non-resitant plugs are the key, or if the plug wires are that way, but it does help. And if there's a break in one of the wires that could do it as well...
HTH

J.R. is on the right track for the CB. the inline fiklters can help some for CBs, but a lot of timeyou'll get RF intereference from the plug wires, cap&rotor. spark jumping causes a lot of this. try the inline filter thing cuz its cheap and might fix it for you. if not, you ought to try to plug wires cap and rotor

Thanks guys. My dad and I will try the stuff.

Do you have an aftermarket system installed? An amplifier maybe?