There is one, a [hwrng] process, but I don't think that's it. It's also in D state on other virtual machines on the same host without this symptom.

(The process is probably from virtio-rng.)

I am assuming the guest (and host) kernels are sufficiently recent? I remember older kernels having a bug with load calculation. Does disabling Virtio-rng help? D state processes will cause rise in load average depending on NRCPUs.