their are several reasons why this might happen, but this did fix my problem.

it always had this problem, but i realized after i recapped the board it got worse. when you boot it, and it goes through post and beeps for each stage, the first beep was VERY loud... the next few would be quieter until it settled to it's setpoint volume. had nothing to do with the volume pot either, as i replaced that.

then i recapped the board as all the 37 year old electrolytics were still there. now the volume is super loud for most the boot sequence. loud enough it was probably going to blow the speaker, wake the neighbors, etc... it settled down much slower than before. so at first i think perhaps the 12v line or grounds were suspect... perhaps the new capacitors drew more energy when first powered on holding the 12v line down longer before it stabilized... no dice tho, it gets upto 12v at the test point instantly. so now i go and read up a little about the sb 300 and came across a pretty good writeup about testing and what the chips do, theory of operation and whatnot. think i googled sb300 troubleshooting/diagnostics or something like that. anyways, i took a good look at the schematics for it and discovered one of the capacitors i replaced (it was c13, 47mfd) was for smoothing the volume pot's output to the volume attenuator chip...

i learned that replacing stuff with a slightly larger value without looking at the purpose of the capacitor, was not always going to be a good idea. at first i replaced it with a 100mfd which is what i had on hand. then today after more research i tried out a 10mfd instead since i wanted it to stabilize earlier over smoothness of the volume pot. it actually seems to transition just fine anyways, so idk why they put a big cap there, apart from the fact that it may have been desirable to know if someone's playing with the power switch to try and get the memory to garbage itself and put free credits on the machine... could also be that something else is wrong on the sb still, like the volume stepper chip doesn't get full voltage, and putting a smaller cap in means it was easier for it to pull up on powerup than a larger one... idk. did not test the volts on the chip, but tried the cap swap first and it worked out great.

SO! if you have a sb 300 or similar design where a cap is used to smooth the input to the stepper chip, and you hate that obnoxious loud first few beeps on the machine when powering up, seems like c13 is your ticket replace with a 10mfd 20v. it now stabilizes before it posts. cheers ya all.