iMac G5 sound issue

I have a rev. A iMac G5, and it works great other than the fact that occasionally some system sounds (trash emptying, notification popup, etc) will be replaced with what I can only describe as a short, sudden buzz. Sometimes it happens but many times it doesn't, and if you have the speakers turned up to any reasonable volume it can be startling. I've tried to research the problem and even reset the PRAM in case that may have helped but to no avail. Anyone have an idea about this?

Ps. The iMac had the PSU and logic board replaced a year ago because of the infamous leaking capacitors, but I don't think it has anything to do with the issue.

Intermittent problems are usually the most difficult to resolve, especially if it turns out to be hardware. You've already reset the PRAM so I guess the next step would be a backup and reinstall to eliminate any software issues. If the problem persists and remains intermittent, I would just live with it. If finally the sound goes out altogether, then it might be worth taking it in and having it repaired.

Regards.