Valmiki Ramayana Yuddha Kanda Sarga 55 Shloka 13

तस्यरक्षसः that Rakshasa, राक्षसैःसह along with Rakshasas, तथा like that, निर्गच्छदः going, सागरम् ocean, क्षोभयन्निव agitated,, सुमहान् नादः huge noise, बभूव rose.

While that Akampana was going like that along with Rakshasas huge noise that arose was as if the ocean was agitated.