Full Bridge SMPS

[Fank1]

I'm building a switch mode supply, rather large.
Full Bridge 3KV @ 1A out.
I've got the snubbing across the mosfets to acceptable levels.
BUT I notice switching spikes across the primary of the transformer at turn off equal to the on voltage with no current flowing.
Should these be snubbed also ?? If so to what practical level?
Thanks

[T3sl4co1l]

Flyback of the leakage inductance?

If it's not doing anything, does it matter?

Tim