Si dangling bond centers in aerosol particles of amorphous hydrogenated silicon formed by thermal decomposition of SiH4 in Ar were studied by pulsed electron paramagnetic resonance. The hole-burning and inversion-recovery experiments demonstrate that large-scale rapid spectral diffusion takes place in the samples with high spin concentration. Correlation times τc of the spectral diffusion and spin-lattice relaxation timesT 1 were obtained in the temperature range between 77 and 290 K. Above 130 K, τc andT 1 are proportional one to the other. The unusual feature of this spectral diffusion is that the shape of the central part of the spectral hole does not change when the delay time increases. The other paramagnetic centers previously investigated showed a remarkable change of the hole shape which was induced by modulation of dipolar interaction due to spin flips. It is suggested that the observed anomaly in the Si dangling bond centers arises due to cooperative spin flips.