How can I identify the clusters of a grid pattern noise in the modulus of my image Fourier transform and filter out this noise?

Hi everybody! I'm a newbie using Matlab image processing toolbox. I would appreciate some help to solve my problem or have an explanation about some concepts. I have a DICOM file containing a tagged MRI image. The image has a pattern grid noise overlapped.I'm trying to identify the cluster related to the grid in the modulus of the image FT I've computed(attached below), beasides finding a good frequency filter to remove the grid. My problem is mostly related to the fact I have no idea about the cluster concept. Thanks