'98 Honda Accord Loud Transmission Noise

I have a 1998 Honda Accord EX V-6 (~135K Miles). Sometimes when I shift
the car into reverse, it makes a very loud noise (as in so loud, that
passengers will sometimes gasp slightly). I've taken it into my
mechanic, but since the noise is intermittent I can't reproduce it.
Does anyone have an idea what this could be or how I could be of
assistance to my mechanic in diagnosing it?

About the noise:
It sounds kind of like a *CRACK* or a very pronounced click. I *THINK*
it happens after the car is already in gear. It only happens when
shifting into reverse.

Thanks

 

I forgot to mention, it's an automatic transmission (though I think
this car is only available in automatic anyway.)

 

Does service schedule require changing a-t-f filter ?
www.aa1car.com/library/2002/bf90222.htm para 12

 

There is no filter that has to be changed or cleaned. The Honda fluid is
drained and refilled only with Honda branded fluid.