Atomic force microscopy when used in its imaging mode is a technique which allows surface structures of biological membranes to be resolved, in principle, with molecular resolution (Fotiadis et al. 2002). By using the reflection from the scanning cantilever, sub nanometre changes in the surface height can be detected during scanning. This signal forms the feedback signal intrinsic to the scanning microscope. In addition to XY imaging modes, the technique has been used to study hair cell lateral membrane elasticity (Zelenskaya et al. 2005). The time dependence of surface fluctuations can also be measured and it has been reported that yeast cell membranes undergo oscillations of 0.8 -1.6 kHz (Pelling et al. 2004). In order to investigate whether hair cells also show membrane properties found in yeast,and important to the understanding of some models of cochlear mechanics, we have investigated the surface membrane of guinea pig cochlear outer hair cells microdissected from the organ of Corti. Isolated outer hair cells from the apical (low frequency) turns are cylindrical and 50-80 μm in length. To hold the cells during scanning and limit rolling, tapered 100 μm long slots 10 μm deep etched onto quartz slides were used to prevent cell movement during the cantilever contact. Force-distance curves could thus be obtained from the lateral membrane. Using the quadrant detector of the microscope (Nomad, Quesant Instrument Corp., CA, USA), both the z-motion (flexion) and the x-y (tilt) motion of the cantilever were measured. Standard V shaped cantilevers (stiffness 0.01 N/m) were used attached to a purpose-built holder which allowed scanning under solution. Spectral peaks distributed between 1-7 kHz were recorded in the noise of the reflected light in both flexion and tilting motion of the cantilever. Tilting (x-y) motion noise peaks were prominent in measurements made when the cantilever was either immersed in solution or touching the hair cell membrane. The power corresponding to tilting motions was reduced by over 20 times when the cantilever was withdrawn into air and z-deflections mainly occurred. In measurements made on cantilevers placed in solutions with viscosity between 1-800 cP (0.001-0.8 Pa.s), a redistributon of noise power was also found between tilting and flexion modes. The results indicate that understanding the complex dynamics of such cantilevers (Sader, 2003) may be critical in biological applications to prevent attribution of spurious signals.