"I planted it, after amending my soil..."

That was a mistake. Next time you plant a tree or shrub, DON'T amend your soil!

"Then we had (a) lot of rain, I mean a real lot..."

Have you been checking your soil to see if it's drying out in between rains? The combination of poorly draining clay trough you made by using amended soil and the excessive rain may be causing an over-watering situation, or, maybe not.

"Is this bad, is my vi(b)urnum in trouble, and if so, what can I do to help it out?"

Well, that's hard to say with the info provided. What makes you think your viburnum isn't just dropping its leaves for winter? I would imagine that's happening quite a lot in zone 5, by now.

Here is a link that might be useful: Planting a Tree or Shrub

I agree that the shrub is most likely going towards it's normal leaf drop. Bet it will do just fine. You can work on improving the clay soil in that area to help this shrub and other future plantings by putting down organic mulch now - shredded leaves are great and in good supply. If you want a weed barrier for the area you could also lay down cardboard or sheets or layered newspaper before the leaves. Earthworms will increase and incorporate some of the organic matter into the soil.
Rachel

Thank you both for your responses. The reason I didn't think it was just a normal leaf drop is due to the color of the leaves, almost looks as if they have a disease, and also the fact that none of my other shrubs in that are are dropping leaves. Beside the Blue Muffin is a Cranberry Viburnum trilobum �J.N. Select', a Winterberry, 'Jim Dandy' and a Hydrangea 'Pinky Winky' and the leaves on all of these seem to be fine, no discoloration and none falling off yet.

Tell me, why was it a bad idea for me to amend the soil before planting the Blue Muffin? I mixed some Bumper Crop in with my clay soil and I thought that was a good idea.

Linda

Linda, if you amend only the soil you use to backfill, your plant will do well for a while. But the the planting hole is kind of like a of a flower pot. The plant will start sending out roots, but when they reach the limits of the nicely amended soil you backfilled with, they will have difficulty expanding into the harder clay around them. Then the roots can start circling around in the planting hole instead. So then you can have a somewhat root bound plant, not growing as large or as healthy as it should. So, amending general areas is better than amending a specific planting hole. The bumper crop sounds like a nice product - sounds compost-like with the worm castings. I think you would like the effect of shredded leaves as mulch. Earthworms also love used coffee grounds sprinkled in there.
Rachel

There are multiple reasons not to amend the backfill soil for woody plants, but poor drainage is the primary reason. Numerous studies have shown that amending backfill soil, when planting trees and shrubs, is detrimental (or, even in best cases, of no long-term benefit) in almost all cases. Studies with native soils ranging from sand to clay, and with amendments ranging from manure to ground bark to perlite, all contraindicate the practice.

The Myth of Soil Amendments by Sustainable Horticulture

The Myth of Soil Amendments by Dr. Linda Chalker-Scott

P.S. If you do amend your soil, always do so very lightly (like using less than 5% of some organic additive) so as not to significantly negatively impact drainage.

One other comment on your blue muffin - viburnum beetles will probably be a problem, since you are in MA, not far from me. This species of Viburnum (dentatum) is their favorite, to the point that the leaves of mine looked so unsightly so much of the time (full of holes from the caterpillar-like larvae) that I just finished removing it. I also didn't want the Viburnum beetles to move to any of my other Viburnums, and since this time of year the eggs are in the twigs and I think the adults have been killed by freezing weather, this seemed to be the best time to remove and burn it.

Here is a link that might be useful: Cornell U info on Viburnum leaf beetles

Oh lord, I do not want the leaf beetles, that's for sure. Now I'm wondering if it would be best to just get rid of it. I was actually thinking of adding a pollinator to that area but now I doubt very much that I will. It is located right next to a Viburnum Cranberry JN red-wing and I do not want that to be affected.

Thanks to all of you, you've really been a huge help to me.

Linda