How often should I see OSPF LSUs?

I am working through an issue and need a sanity check... shouldn't i only see a few of these an hour? i am seeing 3-5 every few minutes and I think it the reason why I am dropping OSPF routes that are being redistributed by my firewall(s). I was hoping someone could shed some light onto this... Google tells me what they do, but my assumption is that I should only see one for every OSPF node every 30 minutes.

Thanks in advance