Peavey TNT 115 Oscillating

[rf7]

This amp has a 53Khz noise/oscillation (it kind of looks like a square wave) on the output which makes a weird buzzing sound, that I determined is coming from the Chorus circuitry in the preamp. If I pull U13, the 555 timer chip, the chorus is inactive and my noise/oscillation goes away. And I see a 53Khz spike on my -16V rail also. Anyone seen this before? Any ideas?

Thanks.

[lowell]

Can you post a schematic? Have you tried a new 555?