Azizi, "bul bul" is probably "bulbul", which is indeed something
nice, as you hoped.

According to Wikipedia,

Bulbuls are a family, Pycnonotidae, of medium-sized passerine songbirds. Many forest species are known as greenbuls, brownbuls, leafloves, or bristlebills. The family is distributed across most of Africa and into the Middle East, tropical Asia to Indonesia, and north as far as Japan. and lots more.

Dave Oesterreich