tep... tep... noise when idling and slow going

[dricas]

Hello^^

My 2000 boxster S has some noise like 'tep, tep, tep' when idleing and slow going T.T

It's not airconditioner fan sound, when I off aircon, still tep tep.

after run and stop in parking lot, I can heard that.

about over 2000rpm, I cannot hear that tep tep sound.

Sometimes, keep idleling start 'tep..... tep.... tep....' and after it comes more faster 'tep tep tep' and sound disappear,
but, after high rpm and keep idleing, sounds comes again slow 'tep..... tep.... tep'.... and repetition comes faster... and sound disappear.

I search many articles in this forum...

I guess... do my water pump have noise, like this?

I can hear it at night or indoor parking lot. cuz sounds small.
It's smaller than radiator fan working sound in back of passanger seat.


How do you think about this noise??
Is it water pump noise?

thx for reading my poor question.