Quasi-periodic pulsations ( QPP ) are often observed in X-ray emission from solar flares . To date , it is unclear what their physical origins are . Here , we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 28 October 2013 . We focus on the character of the fine structure pulsations evident in the soft X-ray time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission . We find that during the impulsive phase of the flare , high correlations between pulsations in the thermal and non-thermal emissions are seen . A characteristic timescale of \sim 20 s is observed in all channels and a second timescale of \sim 55 s is observed in the non-thermal emissions . Soft X-ray pulsations are seen to persist into the decay phase of this flare , up to 20 minutes after the non-thermal emission has ceased . We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from \sim 40 s up to \sim 70 s. We interpret the bursty nature of the co-existing multi-wavelength QPP during the impulsive phase in terms of episodic particle acceleration and plasma heating . The persistent thermal decay phase QPP are most likely connected with compressive MHD processes in the post-flare loops such as the fast sausage mode or the vertical kink mode .