if you're not drawing significant current and just want to test a filter circuit, use a signal generator with 2 channels: 1 to produce the sine wave, 1 to produce the noise, then connect them in series. if you only have access to a single channel signal generator, try some of the noise generator circuits which use the 74 series logic to make white / red etc. noise, the reduce the amplitude (maybe with a potential divider followed by a buffer amp) and again, connect the outputs in series.