foolin

Hello, i recently bought Jaguar X-Type 2002, 2.0 petrol. Some strange sound is coming from air intake, i dont know how to describe it exactly, it's like some guggle noise. It comes for a few seconds when i let go gas pedal and engine goes idle. The sound is there for a few moments and then goes away.. English is not my native language so sorry for mistakes:) Any help would be appriciated, thanks