Bizarre...
1048:
As Roscal says, no 50HZ fundamental for this one?!
Also note the cutoff at 7k or so (same for the other pumps) this is due to the mic and/or codec, and will have an effect on the perceived noise - of the D4 in particular
DDC:
small spike at 58Hz, moves up to 62Hz when the pump speeds up. 3480->3720rpm?