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Need some direction on where distortion is coming from on a Donkey Kong 2 that I'm working on for someone (not my game)

Symptom:
Higher frequency sounds seem ok, but when there are lower frequency sounds (ex when the monkey stops he's feet) it sounds a bit crackly / distorted (see video below).

Background
He bought the game and the sound was VERY soft...almost couldn't hear it. Looking through the audio amp on the Sanyo 20-EZ, I noticed someone tried refurbishing it and accidently switched the power transistors (PNP swapped with the NPN and vice versa).
I went ahead and put in new transistors and e-caps (the right way) and the sound volume is great, but the lower frequency sounds get a little distorted. I don't know if this was like that before someone tried fixing it, or the amp is still the problem, or the PCB has an issue, or the speaker etc. He said it's a new speaker.

Resolution:
It was the audio amp, specifically R383 (39 Ohm fusible resistor).

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