I'm going to move the system over to another game. Still not entirely happy with the AIQ audio, but Stern's own audio seems to be the root cause of the crackling. Below is from the AIQ owner's thread and is exactly what I'm hearing. So, I don't think upgraded speakers and an amp is needed on AIQ. I also prefer to change the volume with the coin door controls instead of on the amp. Turning down the coin door volume causes the audio to cut in and out, minor inconvenience, but still inconvenient to look inside the cabinet for the amp and change the volume there instead of the coin door.
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Quoted from Sleal16:
Curious, hows most people's sound quality on the game? Since I got the game, its had some persistent rough artifacts kinda sounding like crackling. With most of the audio its a little subtle but with louder voices and other clips its more apparent. At first I thought it was the speakers and I was going to deal with them at some point later, but when I installed the headphone jack and had a few games off of that, its the exact same. I tried changing some of the random settings but still can't seem to clean it up. Not sure where to look exactly.
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Yeah, me and a couple other Pinsiders have this same issue. I upgraded my speakers to Pinwoofers and I still get the "crackling" sound... Seems to be just a flaw in the game. They might address it with the new code that includes insider connected but who knows.