Honestly every single v6 in our years does this. Mine has always done it and I'm not gunna spend 500 to fix it since that's not guaranteed to make it stop even once I've paid to install all new stuff and flush it.
Yeah the noise sucks but it's a problem we may have to live with. If someone figured out the exact thing that causes it I probably wouldn't spend much time and money on it. Instead just sped it on HP mods
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1999 V6 Mustang Dark Satin Green , SR CAI, BBK 65mm Throttle Body, Screaming Demon Coil Pack, SR Lowering Springs, Pioneer Stereo, 2 12' inch subs and 1600watt amp, Green Calipers,