I think he replaced the antenna, not the head unit.
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Welcome to Genvibe blueskyflyer. Remember when flying, fly in the middle of the air
The only time I ever ran into something like that was when I was using an FM transmitter to play music from my phone over the car radio. Those things are built cheap, and they emit a broad band of signal, wiping out over the air signals even away from the audio transmitter's supposedly tuned frequency. Sometimes a ghost of the commercial signal could get through, but very faint. Even then, the affected range of interference was under 10 MHz, the transmitter tuned to say 88.1 MHz had no effect on on the 100+ MHz stations. If yours is the same across the full band, its not likely a transmitter interference.
The antenna base has a built in amplifier, but if that's not working, then its the AM band that suffers most.
If you can't figure it out otherwise and decide to get a used replacement radio, be sure that it came from a Vibe or a Matrix. GM used other radios that look the same, but they require connection to a GM car data bus that the Vibe, being mostly Toyota, doesn't have. You might find one nearby from a junkyard, check car-part.com Around me they list some as cheap as $30, but a lot of these radios get the paint rubbed off the buttons. Its not too hard to replace the radio, or to swap buttons between them. If you get really lucky, you might even find a nearby genviber who'd be willing to do a temporary radio swap to help diagnose the issue
If you go for an aftermarket radio, I'd recommend one with bluetooth. I also have a car with android auto, I'm addicted to that too, but that feature jacks up the price of aftermarket units