肚子 + 咕咕叫
咕 (gū) is an onomatopoeia representing a rumbling or gurgling sound. It is most commonly reduplicated as 咕咕 to imitate the sound of a stomach growling (肚子咕咕叫) or a pigeon cooing. Like many Chinese onomatopoeia, it is typically doubled for a more natural and vivid effect.
中午没吃饭,肚子咕咕叫个不停。
Zhōngwǔ méi chīfàn, dùzi gūgū jiào ge bù tíng.
I didn't eat lunch, and my stomach keeps rumbling nonstop.
窗外的鸽子咕咕地叫着,听起来很悠闲。
Chuāng wài de gēzi gūgū de jiào zhe, tīng qǐlái hěn yōuxián.
The pigeons outside the window were cooing; it sounded very leisurely.
他肚子咕了一声,尴尬地笑了笑。
Tā dùzi gū le yì shēng, gāngà de xiào le xiào.
His stomach gurgled once, and he smiled awkwardly.