The headphone jack is sending way too much gain to the poor input jack of the laptop.
If you have a volume knob for the headphone jack turn it way down low and try again.
Why dont you just use the RCA cinch jacks at the back of the cassette player?
They should deliver the correct current for your needs.
And sometimes you have to switch from microphone to line levels in the audio controlcenter of the laptop.
Hope that helps...
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