This paper deals with the modelling and simulation of combined phase and amplitude noise for QAM direct conversion receivers (DCR). We show that, due to phase noise, there is a cross coupling of quadrature component of the signal as well as quadrature component of amplitude noise to in-phase component of signal. Similarly, there is a cross coupling of inphase component of signal as well as in-phase component of amplitude noise to quadrature component of the signal. Based on the analysis, the symbol error rate (SER) for different levels of amplitude noise as well as phase noise values are presented for M-ary QAM modulation schemes. It is seen that for small phase noise, the SER approaches theoretical SER for only amplitude noise case and increases to large values for large phase noise.