Robot-assisted minimally invasive surgeries (RAMIS) have many benefits. A disadvantage, however, is the lack of haptic feedback. Haptic feedback is comprised of kinesthetic and tactile information, and we use both to form stiffness perception. Applying both kinesthetic and tactile feedback can enable more precise feedback than kinesthetic feedback alone. However, during remote surgeries, haptic noises and variations can be present. Therefore, toward designing haptic feedback for RAMIS, it is important to understand the effect of haptic manipulations on stiffness perception. We assessed the effect of two manipulations using stiffness discrimination tasks in which participants received force feedback and artificial skin stretch. In Experiment 1, we added sinusoidal noise to the artificial tactile signal, and found that the noise did not affect participants' stiffness perception or uncertainty. In Experiment 2, we varied either the kinesthetic or the artificial tactile information between consecutive interactions with an object. We found that the both forms of variability did not affect stiffness perception, but kinesthetic variability increased participants' uncertainty. We show that haptic feedback, comprised of force feedback and artificial skin stretch, provides robust haptic information even in the presence of noise and variability, and hence can potentially be both beneficial and viable in RAMIS.