recent bahaviour change in my dog

Question
I have a 3 yr old havanese (not neutred) and until recently never bared his teeth to me.  However, he has started to grown and snap at me when I try to trim the hair around his eyes or backside.  I have done this many times in the past without incident.
He always likes to get his belly rubbed, but sometimes he will  growl  even  when he willingly rolls over to be rubbed.
It seems so out of character.   I am afraid to take him to be groomed in case he tries to bite the groomer.  I wonder if he had bad experience at the groomer previously and she did not mention it.  

Answer
Groomers contribute HEAVILY (HEAVILY!) to grooming problems in dogs.  There are many very bad groomers.  The best approach to having a dog groomed is to question the groomer extensively regarding his/her experience with behavior problems and then INSIST on being present for (at least) the first grooming (by present I mean IN THE ROOM.)  Additionally, dropping a dog off to pick it up several hours later is never a good idea.  If you are out in the waiting room (and the groomer KNOWS you're there) your dog will have a much more pleasant experience.

As for your dog's aggression toward you (especially with the belly rub), I suggest you attempt to rehabilitate him to the presence of the scissors (and do NOT offer belly rubs at all for the unforseeable future.)  The belly rub problem might not actually be related to grooming but rather submission; oddly, dogs who offer bellies to rub also can accompany that with a dominance or fear related avoidance behavior (growling or even snapping).  As for the scissors, never under any circumstances provoke aggression.  Instead, attempt to associate scissors with something very positive and rewarding.  If your dog likes to play with you, take the scissors out for a few minutes just prior to play time.  If he has a special treat he loves, put the scissors in plain sight, wait a few minutes, then offer a treat (after asking him to perform a behavior such as "sit") then put the scissors away.  When he shows absolutely no response (negative) to the presence of the scissors (and in fact might begin to associate their presence with something good, which you will know by observation), begin to scissor the air near him while offering a treat (so long as his body posture demonstrates that he's relaxed, not anxious or fearful).  I think if you do these things carefully, within a few weeks your dog should begin to allow you to VERY BRIEFLY use the scissors on him (one hair at a time at first!)

Meanwhile, you need to learn something about dog psychology and the absolute best place I can send you is to Dr. patricia McConnell who has several books available on this topic and positive reinforcement training.  AND..........get your dog neutered ASAP!  he is NOT a candidate for breeding.