Unusual noise in the data

I work with UXO land data acquired using Push Cart.
For last few projects, I have seen presence of an unusual noise while I am gridding the raw mag data. It is alternating high and low mag value like a stripping in the data. This noise is being reduced once I run non-linear filter on the data. However, I would really like to know what factor is causing this. 
Please see the attached presentation. Example is attached.
Any help would be greatly appreciated.
Thank you,