Sounds like the odor of hot or burning antifreeze.
Maybe during your flush, some got spilled on your exhaust-system.
Or a heater-hose/valve sprung a leak and it's dripping on your exhaust.
Worst case - Your flush caused seepage from a weak heater-core and you're now experiencing the odor of hot antifreeze evaporating. This is often accompanied by severe windshield fogging when operating the defroster.

Happy Motoring, Mark

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DrDKW