This paper introduces the modelling and characterisation of the noise properties of the vertical cavity surface-emitting laser (VCSEL) coupled in lateral direction with a passive cavity. This design of VCSEL with this transverse coupled cavity (TCC) is proposed for high-speed photonics. We introduce comprehensive simulationson the influence of the induced lateral slow light feedback on the relative intensity noise (RIN) and carrier-to-noise ratio (CNR). The proposed model incorporates multiple round trips of slow light in the TCC as time delay light in the rate equations of the VCSEL. The obtained results are compared with those of the conventional VCSEL.We show that the noise performance of the TCC-VCSEL is optimised when the VCSEL exhibits stable continuous wave (CW) operation under strong slow light feedback and the TCC length is smaller than 8 $\mu$m and between 11 and 13 $\mu$m. When strong slow light induces unstable regular and/or irregular oscillations, RIN is enhanced and CNR is lowered.