Randomly Aggressive Beagle

I have a 2 year old beagle and a 7 year old black lab. They both get along well 90% of the time but occasionally the beagle will become EXTREMELY aggressive towards the lab and nobody else (when he snaps I can pull him aside and hold him infront of me and he will growl and literally tremble for several minutes, but never at me - i've gotten inches from his snout and stared him down during this or even kissed him out the nose. Hes also never acted this way with my brother's dog when it visits, only my black lab)

They're both male dogs, neither are fixed and I'm led to believe it may be a dominance issue because the beagle spends a lot of time "dominating" the lab.

It's hard to tell what triggers the aggressive fits usually hell just slowly start growling and then sniff the lab as he growls and usually starts biting and attacking it after sniffing the labs ears. After an episode I'll separate the two dogs and sometimes he'll be nice when i let them out, and sometimes he'll continue to be aggressive for as long as a day.

Is this a dominance issue? Any ideas?

yes.. Get them neutered....nuff said...

I agree, get them both neutered preferably before you end up with a very injured dog! I would also not recommend treating his agression by "staring him down" as that itself is a very agressive mood in dog language and you should be giving behaviour to reduce the tension not adding to it. Instead give both dogs "time outs" and work on using methods like NILF to establish yourself as a calm leader.
http://www.pets.ca/articles/article-dog_nilf.htm

attacking it after sniffing the labs ears.It might be worth while having the Lab's ears checked for infection. Smells of infection in one dog have been known to trigger reactions in other dogs. Really, I'm guessing this sounds too easy, but, as I said, maybe worth a try?

This is a classic case of dominence due to them not being neutered.

If you want to instill balance, harmony and just general good health for your dogs, then get them fixed.