Pain when pooping (Male Angora)

Question
Dewey, my rescued male Angora for the most part has been quite happy and healthy. I have bonded him with a female Lion head I have originally had to provide her w' a little company. They are both about 4-5 yrs old. They get along fine (both are fixed). I am very familiar with GI stasis issue due to early run ins with my Lion head, a few visits to vet to insure no blockage, Oxbow critical care, metacam, Metoclopromide regime etc...nursing her back to a happy binkying bunny.
Now with Dewey, the male Angora, the other day I started noticing some teeth grinding, it occurs when he is in the process of pooping (both cecotrops and final poop). I spoke with my vet (rabbit specialist), who will be stopping by in a day or so due to her busy schedule,I have left over metacam (still good not expired) from Simba, weigh is similar, was asked to provide him with this for the moment.
As for his other actions: Poop (both types) are normal, healthy looking, still eats and drinks well(he eats like a horse). Diet is same (I use a dessert dish, one for each, they eat separate because one will always finish before the other and go into the others dish.)It has a mixture of greens(spring mix as it is called, but I remove the spinach due to its higher oxy...something, and calcium content)and it is mixed with size/amount appropriate Kaytee Timothy hay predominant pellets (Timothy plus with no alfalfa), 1/4 cup sized scoop for him, a bit less for her (she is smaller). I give this to them twice daily, morning and evening, plenty of Timothy Hay and Apple sticks to munch and gnaw on daily in between, as well a sliver or two of Granny Smith Apple as a snack upon coming back into house from their daily outdoor romp. They free roam the house (Very bunny proofed...I think they own the house and I just hang out lol). No sign of any ingestion of any foreign substances ( no carpet digging/chewing). I'm stumped at the moment at what is causing this discomfort. I gave him a dose of the metacam first one thus far (one syringe daily w' 3 ml dose, tiny syringe), he even wanted to go outside after his breakfast like normal, he munched a bit, even threw out a binky or two ( it's getting chilly here in VT now) and seemed content. After going back in, hopping into litter box, again, signs of discomfort ( teeth grinding, or lip smacking, licking his coat, facial expression changes etc.) This was about 30-45 min after giving dose after their breakfast, not sure how long it takes to work. Im stumped.
Due to his discomfort, he at times will shoo away Simba as he had done early in their meeting, even getting a bit aggressive with ears back and a small chase ensues, which ends amicably for the most part. Shortly after they sit side by side nibbling upon the apple sticks, or with her grooming his coat, licking his nose etc.
I feel bad that he is going through this and will be getting to the bottom of it shortly, but I had a minute to dwell upon this and saw this site, figured it couldn't hurt to fill my noggin with any and all input I can acquire.

Thank you so much for any thoughts you have.
Most Sincerely,
Kirk

Answer
Dear Kirk,

That's a pretty unusual problem.  I don't think I've ever heard of anything like this before.  I guess there are two possibilities:

1.  The tooth grinding you are hearing is actually tooth purring, and he's having a Cecotrope Moment that he doesn't like to have disturbed.

2.  He is experiencing discomfort when he poops.

If it's #1, then no worries.

If it's #2, then the only thing I can think of that might cause this would be an anal polyp that's up in the rectum where you can't see it.  Those can cause a bit of discomfort, but I have no idea whether it would be enough to make him cranky while he poops.

If all else seems fine, then this may not be anything to worry about.  But I hope your rabbit-savvy vet was able to get to the bottom (ar ar) of the problem...if there is one.

Wishing you happy, healthy buns,

Dana