Some DVM's have trouble with AC volts at higher frequencies. Some don't go over 1kHz, others may go over 1Mhz. Most will work well and are calibrated at lower frequencies around 50 or 60Hz in line with mains supply frequencies.
You will need to check the spec.s for the meter.There may be an issue with how the meter derives the rms value. Some use "true rms" others use averaging which will not work for pink noise.
Regards Philip