This paper describes a fast method to estimate crosstalk noise in the presence of multiple aggressor nets for use in physical design automation tools. Since noise estimation is often part of the inner-loop of optimization algorithms, very efficient closed-form solutions are needed. Previous approaches have typically used simple lumped 3-4 node circuit templates. One aggressor net is modeled at a time assuming that the coupling capacitances to all quiet aggressor nets are grounded. They also model the load from interconnect branches as a lumped capacitor and use a dominant pole approximation to solve the template circuit. While these approximations allow for very fast analysis, they result in significant underestimation of the noise. In this paper, we propose a new and more comprehensive fast noise estimation model. We use a 6 node template circuit and propose a novel reduction technique for modeling quiet aggressor nets based on the concept of coupling point admittance. We also propose a reduction method to replace tree branches with effective capacitors which models the effect of resistive shielding. Finally, we propose a new double pole approach to solve the template circuit. We tested the proposed method on noise-prone interconnects from an industrial high performance processor. Our results show a worst-case error of 7.8% and an average error of 2.7%, while allowing for very fast analysis.