When Dave Medeiros started working at the West Tisbury post office three years ago, some things were bound to change.

For one, there was the name problem. Another Dave - Dave Chickering - was already working there, and the computer chip in the postal cash registers wouldn't accept two Daves keyed into the system. That's when Mr. Medeiros officially became Big Dave.

Another thing about to change with Big Dave's presence was the audio equipment. Mr. Medeiros took one look at the Toshiba transistor with its bent antenna and said, "This can't do."

Armed with a gift certificate he won from the United States Postal Service for selling a high quota of telephone cards, Mr. Medeiros sailed off to the nearest mainland Sears outlet.

"For an extra 20 bucks, I got us a nice stereo with tape and CD," he says.

Thus began the transformation of the West Tisbury post office into something less like a federal outpost and more like an FM-radio station. If you notice anything upon walking into this place, it's the music.

Nothing like you'd hear in an elevator or a dentist's office, this is pop music with a play-list driven by the tastes of both Daves.

"Dave's into reggae, I'm into heavy metal," says Mr. Medeiros. "But I like to listen to a lot of stuff like Latin music and salsa."

In many ways, the unlikely music scene that has evolved at this post office is just an extension of the two men's friendship. You get the feeling that these two guys shared a dorm room back in college and simply decided to replicate the scene on the job site.

They were, in fact, friends before they landed in the same small post office in West Tisbury. When the two Daves first met, it was at the Vineyard Haven post office back in 1995. Mr. Medeiros was the newcomer, and Mr. Chickering, who had grown up coming to the Island in the summers, helped Big Dave get his first apartment on the Island.

"I can't say enough about Dave," says Mr. Mederios.

When they're not sorting magazines and catalogues, weighing mail or selling stamps, the two men share deejay duties. The age spread between the two is 10 years. Despite the moniker, Big Dave is actually the junior of the two at 32 years.

Sometimes the musical choices can clash. "I put on a CD from the seventies," says Mr. Chickering, "and he'll give me a look so I feel like an antique."

But there's no fighting going on. If anything, these two postal workers have channeled their musical energies outward to their colleagues and customers. It's a good day if their choice of tunes can put senior staffer Antone (Tony) Rezendes Jr. in a good mood.

Mr. Rezendes, who is 58, admits that his musical preferences and knowledge are firmly lodged in the late 1950s. But that doesn't mean he's immune to what's in the air.

"I put in something I know Tony's never heard," says Big Dave, "and all of a sudden I catch him whistling along to it."

Even better, say Dave and Dave, is when customers get into the groove.

"The funny thing is, we listen to so much music that the customers bring in music," says Big Dave. One woman went away on vacation and left them her collection of CDs.

"It's nice to put on an obscure CD and hear someone say, ‘I haven't listened to that since college,' " says Mr. Chickering.

This atmosphere is helped along by the simple fact that this post office is tiny, and sound doesn't have to travel far. "We call it ‘Das Post Office,' " says Big Dave, referring to the cramped quarters.

So, what songs top the charts at the West Tisbury post office? According to Big Dave, the B-52s and Bob Marley are the most popular with postal patrons. But back on the shelves amidst the official postal paraphernalia, they've got dozens of CDs - the Cure, Steely Dan, U2 and Duran Duran standing out among the selection.

Big Dave, who once headed up security at the Hot Tin Roof, also knows his liner notes. He's prone to such remarks as the observation that one of the best-liked B-52s songs, Mesopotamia, was actually produced by David Byrne.

Clearly the more social of the two, Mr. Medeiros is a font of information and relishes the interaction with the public. "In a small town, you get to know everybody," he says. "In summertime, I walk down the street and they might not know my name but they know I'm the mailman."

As for the nickname, Big Dave takes it in stride. "Anywhere else I've ever worked, there's been another Dave there," he says.

Mr. Chickering is a tad more acerbic, but good for backroom banter and one-liners. When someone comments on his soft-spokenness compared to Big Dave, he quips back, "We're heavily sedated at all times."

The humor does not end at the main post office. Back at the old substation in Alley's General Store, the door to the post room and its 154 boxes is a Dutch door. Someone has written above the doorway, "Mr. Ed." Sure enough, the scene looks a lot like the old TV show.

Not that anyone knows who reached up there to write the words, but they all laugh, even postmaster Victoria Thurber, who seems to view the Dave and Dave show with the same reserved bemusement.

Her current crew, she concedes, is a bit more social than others she's had in 14 years at the helm. "We've grown out of the small office," she says, "but we're still trying to run it as a small office."

Two years ago, they added 330 boxes. They now handle some 40,000 pieces of mail a week. But Mr. Chickering points out that this post office has maintained its character in the face of such growth.

"This is Martha's Vineyard's best-kept secret," says Mr. Chickering. "Some of the people bring us cookies." And where else can you find a post office where the name of the postal clerk printed right there on your receipt is Big Dave?