This seems to be output of an unstable system. Does that system use feedback?
Anyway, this interference of higher frequency than the original wave. So, filtering may solve the problem. Note that filtering may distort the triangle waveform a little.
Hi,
Yes, it appears to be a high frequency oscillations in an opamp. If you use an opamp and it requires frequency compensation, use it. Else try with a small capacitor 10 to 100 pf across the opamp feed back resistor.
Regards, Laktronics