We examine the influence of high-frequency hydromagnetic noise in the range Pc 1 to Pi 1 on the stability of low-frequency Alfv¿n and fast compressional waves in an inhomogeneous plasma imbedded in a curved magnetic field. Turbulent diffusion of hot protons caused by Pc 1/Pi 1 noise results in the appearance of an effective ''collisional'' viscosity, which in turn may induce the growth of drift instabilities, but only if the wave frequency is less than Larmor drift frequency. Using ATS 6 satellite data, we obtained some experimental evidence in support of the proposed plasma instability mechanism.