Without hearing it firsthand, I'd say it's normal. The venting is supposed to happen, but when I had a 1998 it was pretty quiet. You had to listen for it inside a quiet garage.

I don't know if a louder purging sound is a sign of any problem, but there have been some threads about that in the past. Watch to see if it gets progressively louder or changes the type of sound.

If there was a problem, it should set off the check-engine light with a code of P1456 or P1457.

 

Thanks JB,
We live in Hawaii also, so that may have a bearing on pressurization. I could drill a small vent in the cap, & that would fix the bugger LOL

 

Don't drill a hole in the cap. That would cause a CEL (P1456) and maybe other problems.

The fuel tank IS SUPPOSED TO DO THAT. Your EVAP system is functioning. It's just louder than normal.