Hello all, I hope I'm in the right place. There is an annoying buzzing interference in my 98 Blazer's FM reception that is being picked up through the antenna that happens when the key is in the run position and/or the engine is running. I have tried different radios, both stock and aftermarket, as well as noise filters on both the power and the antenna, as well as clamping ferrite beads on the leads coming off the computer (if that is where the noise is coming from, IDK) , checking the antenna's grounding, grounding the computer's chassis to the frame, and those didn't help. I can also pick up that interference with any portable FM radio near the vehicle. The AM reception is just fine and it only affects FM. I have also heard this exact buzzing interference in a 91 Corsica, an 86 Camaro with the multi port v6, as well as a 93 GMC Sonoma (all of which I have owned). This seems to be a GM thing.

To help diagnose this issue, I have included an mp3 attachment where I recorded the noise. Has anyone had this interference with their Blazer?

Where is this noise coming from and how do I fix it?I would love to nip this one in the bud.