If you are looking for how much noise level will be for a particular size of trf look in NEMA TR-1 standard. If you are looking at calculation methods from trf parameters ,well it is pretty difficult .Generally speaking,noise level is a function of working flux density in core ( noise comes down with flux density ),weight of core ( noise up with core weight ) ,grade of CRGO used (domain refined or Hi-B grades have lower noise ) ,tank stiffening factors and type of core construction (type of joints ,core clamping etc ) .Manufacturers have their own internal formulae and software programmes for it .Some published papers are also available (IEEE & CIGRE )