Valmiki Ramayana Yuddha Kanda Sarga 65 Shloka 46

तस्यकुम्भकर्णस्य that Kumbhakarna's, एवम् in that way, ब्रुवाणस्य having spoken like that, राक्षसाः Rakshasas, अर्णवम् ocean, कम्पयन्तःइव like agitated like, घोरम् dreadful, नादम् sound, चक्रुः started.

When Kumbhakarna had spoken that way the Rakshasas made noise that was like the sound of an agitated ocean.