Hard to say without more information. Assuming the 328 you note is an E9x rather than an F30, I would bet the residual value used for the outgoing model in the calculation has been lowered causing the the payments to move up. Have not kept up with money factors etc. Just my $0.02...
2011 Space Grey E90 M3, DCT, Comp. Pkg.
1997 Z3 2.8, Artic Silver, Tanin Red interior, MT
1974 2002tii, Inka, 5 sp manual