New here first post. I've got a 2000 volvo s40. A few months ago my front speakers started buzzing, and I lost all audio. Rear speakers worked fine and still do. Decided I would replace the head unit with something a little better. Installed a Kenwood unit and gained my audio back in the front. The only issue is that at medium to high volume there is a popping/buzzing/overall distortion. Mostly durring snare/bass hits. Keep in mind, the speakers are stock, the headunit is not. Today I thought, "hey maybe the speakers are blown" so I installed some Pioneer tweeters and to my suprise!!!! they pop too, no use. So basically my issue is that my front speakers are popping and buzzing at mid to higher volumes. REAR SPEAKERS ARE FINE!
The speakers don't seem to be the issue is what I'm saying. Even the new speakers are popping. The speakers that came with the car are pretty nice. As for the tweeters, they came with a capacitor inline which I'm assuming is the filter.
You can start by defeating (to zero) all tone controls, loudness and else, you may have a number of issues, one possibility (not frequent though) is that the factory speakers don't match the head unit's output impedance, maybe leave the tweeters alone in the front and see of still pops, take a look at those front speakers to see if they are 4 ohm.
the buzzing and popping is caused by the head unit's lack of power (12-15 watts per channel RMS from head units) and the lack of crossovers on the door speakers.
you should put a crossover on each speaker to prevent it from playing frequencies below about 150Hz, and if you want much better performance, consider using a small external amplifier of about 40-75 watts RMS per channel, and replace the speakers with some good separates/component sets.
if you have proper wattage. your issue has to lie with 1 of 2 things ether your wiring has a short or your car has a amplifier from the stock system that's bad and is causing back feed in the system. The tweeters have that cap for 2 reasons 1 is it filters frequencies to a extent, very minimum but the main reason is usually to balance Ohm loads. they use the Cap to even it out. I would still never run a tweeter without a crossover but that's me.