Bad day so far... could it be because of car stereo?

[Trey803 5,000+ posts]

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The alt will not spin any faster because it is "Straining", its speed is regulated to the engine's RPM. Now internally, yes it could be working harder to try and produce more power to keep up, but it will not fall off because of voltage strain.

no, but it would put a bigger mechanical load on the pulley