Hi again, back with another problem. This Duo-R is full of fun.
I've set aside the RGB mod (still out of options) but now have a new CRT that can do NTSC colour, so I can actually enjoy my PCE. While Hucards work fine, CD games have some kind of broken audio effect.
I get this sound across all CD games: in Rondo it's when I press Run on the title screen and when Death charges his projectiles, and in Panic Bomber it's everywhere. Immensely annoying to hear. I've recorded a video so you can hear for yourself: youtu.be/h2Jv4tF1OOs
I've inspected the CD area of the board and everything looks okay. I did a full system recap as part of my RGB mod and I feel qualified to cleanly swap caps. Polarity has been triple-checked, but as this is one sound and not something constant, should I be looking at the ICs?
Any and all help is appreciated.
EDIT: Here's a photo of the underside of the board around the CD area: https://imgur.com/a/jdSCHRg