The nonintrusive detection of particle contamination problems is of great interest to plasma processing in the manufacture of semiconductors. We have studied the influence of particle generation in argon-silane capacitive plasmas on the electrical discharge properties which can be nonintrusively measured with a current-voltage sensor. The Fourier components of the rf current and voltage and the respective phase angles between these signals have been studied up to the fifth harmonic of the 13.56 Mhz rf power. We show that in particular higher harmonics are much more sensitive to the appearance of particles than the signals at the fundamental frequency or the second harmonic. It appears that the observation of higher harmonics is capable of providing early indication of particle growth in capacitive rf discharges.