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# Translation
The speaker squealing is usually caused by three things: loose or damaged wiring, the amplifier clipping, or the speaker itself starting to fail. The first thing you'd have to do is check that all the cables are properly connected behind the radio and to the speakers - sometimes just a tiny thing comes loose and starts that annoying noise. If everything is tight, the problem could be the car's amplifier working with a distorted signal.
Another possibility is that you have the volume too loud and the amplifier is clipping, which is when it goes into saturation and starts distorting the sound - that causes a characteristic squealing. Lower the volume and test if the noise goes away. If you keep having the problem even with the volume low, it's probably the speaker itself that has a damaged coil or a cracked cone. In that case you're going to have to replace it.
If the car hasn't been used for some time, it could also be moisture built up in the speakers - try turning on the radio for a few minutes with the windows open to see if it dries out. But if it persists after a few days, it's more likely to be physical damage or a wire that's actually disconnected.
When did it start - suddenly or gradually? If it was gradual, it's likely the speaker itself is degrading, but there's a detail that sometimes gets overlooked: check if the car's ground (the negative wire connecting the audio system to the chassis) is tight and free of corrosion at the contact points. Turn the system down to a lower volume and see if the noise disappears or stays the same - if it disappears, the problem is often in that loose connection, not in the speaker itself.
Marcelo asker
It started all of a sudden yesterday. I'll check that stuff and test it at low volume. Thanks for the tip!
I had a similar problem in my car and found out that sometimes the squealing comes from a bad connection between the speaker connector and the wiring - it doesn't even have to be an obviously loose wire, sometimes it's just oxidation or dirt causing poor contact. It's worth disconnecting and reconnecting the speaker cables to clean the connectors with a dry cloth before spending money on new parts.
Before you start messing with wires, check if the volume is maxed out or if you're playing music with heavy compression - sometimes the squealing is just distorted sound and we blame the speaker unfairly. But if it persists at any volume, then it could be oxidation on the connectors like mentioned above, so clean the contacts with isopropyl alcohol before taking it to a mechanic.
If none of the above diagnoses match, also consider the speaker wiring insulation - sometimes the wires touch the car's metal body or some corner, and when the car bounces on the road, you get that annoying squeal that seems to come from the speaker but it's just mechanical contact. It's worth poking around behind the panel to see if everything's properly seated, and you can even wrap the wires with some tape or foam if you spot anything loose.
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