Noise correlation is an important topic in radiofrequency (RF) coil design for magnetic resonance imaging (MRI). The original noise correlation formula derived by Redpath showed correlation depends on the real part of the inverse impedance matrix. In this work, we introduce a more generalized formula to include effects from transmission lines and preamplifier input impedance mismatch. This formula is used to calculate correlation between two-channel circuits connected to preamplifiers using transmission lines of variable electrical length. The calculated correlation matches well with that measured on the MR scanner and suggests transmission line length can be utilized as an additional degree of freedom for coil decoupling, and can be adjusted to achieve zero noise correlation.