120 Hz, the last shot was actually 10x sorry for the confusion.
Darn!! I was hoping you'd say 60, which could have meant one of the rectifiers was failing. So much for that brilliant idea!
Are you putting your additional filter capacitance across the actual filter cap, or directly on the regulated output? If directly on the output, it could be confusing the regulator by messing up the response time of the control loop. If you have it across A30C5, then never mind; if not and it is on or near the output and beyond the regulator pass transistor, try to get it onto C5 instead where the circuit expects to have filtration. That might help things out.
And on that note, I really need to crawl off to bed - it's 0300 here in these parts. Good luck, and I'll try to offer more suggestions tomorrow if it's still acting up.
-Pat