Static can come from many possibilities. What kind of static? Analog noise that sounds like ocean waves? Digital noise like popcorn? Usually analog static is introduced in the final stages of audio amplification, digital noise sources are usually rooted much deeper and further up the pipeline. The first thing to check is to make sure you have clean audio power. Not just the proper DC voltage levels that feed the amplifiers, but also check for AC ripple and clean grounding.

You can most likely rule out the boards that were replaced (although that is never 100% guaranteed). Speakers are not usually the source of static. I'd focus on board interconnect cables - especially those that interface CPU sound to sound boards. It doesn't take much to cause a sound problem, a little oxidation or a slightly loose crimp can cause noise problems. So that's what I would investigate next, after looking into the power source condition.

Your welcome. Good luck, hope you get an easy fix.

Check the voltages on the board. On the DC input connector CN2 there should be approx. +12V DC between pin 2 (ground) and pin 6 (+12V) and ­-12V between pin 2 (ground) and pin 3 (­-12V), these voltages come from the Power Supply Board. On the board itself are two voltage regulators to convert the +12V and ­12V to +5V and ­5V for the pre­amplifiers, check these voltages by measuring between the ground (GND test point) and U30 pin 8 for +5V,U30 pin 4 for ­5V.
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Guessing is just a wild card. I'd get an oscilloscope on the audio amplifier and start troubleshooting there.

Could be. I didn't realize you had "good" sounds. So you have static and missing sounds? Is this continuous background static, or is this actually not static, but distorted sounds only with they are played. I might have misunderstood your symptom.

OK. That's probably not the output amplifier section then, especially if you have any good sounds. Your problem is going to be further upstream. I'd seriously suspect any transferred components, such as ROMs.