Are they native InDesign gradients or have they been rasterised in Photoshop and placed back into ID?
What are the values of the banding gradients?
Possibly the most common output setting for a platesettter is a 150lpi line screen at 2540dpi resolution. That yields 256 levels of grey per channel, i.e. 8-bit colour. So with only 256 levels of grey, very subtle gradients over a large area will be prone to banding.
Then you have the additional problem of dot gain, which makes gradients to white particularly troublesome. It's difficult to print an actual 1% dot. The nature of ink on paper will expand a 1% dot in your file and on the plate to maybe a 5% dot on paper, so there will be a noticeable drop-off.