LMFAO
Almost as entertaining as today's Handler's Diary

Needless to say, Mr. Vendor (and his boss) got a quick phone call from me, wherein I pointed out my belief that some village somewhere must be missing its idiot.
Don't follow in his footsteps. Your village needs you...
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since I changed ISP that my routers WAN light goes crazy and does not stop.
You didn't say what type connection you had or have now. Guessing broadband.

With my broadband, my receive light on the cable modem does not stop blinking.
Just haven't gotten around to taping it over yet

Not all the traffic coming into the modem is meant for me, but broadcasts, scans, normal traffic, etc. on the subnet I am on. And yes, some of the scans are directed at me, but my perimeter firewall blocks them. ( you have a perimeter firewall on that router? )

A few times my personal firewall alerted me to an incomeing conection from my isp to port 53.
What firewall? You said personal firewall so it is not the one on the router, but on the client? ( inside the LAN ).
I've seen ZA do this, even though it was configured with the DNS server as trusted, ( go figure ); it was actually a response the client initiated.

Since you are doing research on this, maybe you could tell me this:
How is your ISP ( their DNS server ) sending your client machine these packets when it is behind a router if it was unsolicited? ( I'm assuming two things here, one that your client has a private IP address, and two that your are not using Ipv6. )