Challenging shm

A wedge of inclination θ is rigidly fixed on a horizontal ground and its inclined surface is perfectly smooth.

Now a block of mass M3 is placed on the inclined surface with a light and inextensible string connected through a pulley of uniform circular disc shape, being free to rotate about its axle and with mass M2 and radius r.

Over the pulley, the string is connected to a vertical spring of mass M1 and elastic constant k as shown in the diagram below:


圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Dec09/Crazyshm1.jpg


Suppose that the contact between the string and the pulley is perfectly rough, and now the block is slightly disturbed from its equilibrium position.

Find the period of oscillation in terms of all given parameters (including any extra parameter(s) if necessary.)

Note: The mass of spring is NOT negligible and so it has an effective mass.