Hazrat Mutarrif narrates from his esteemed father (Abdullah bin Shikhkhir), he says: I saw the Messenger of Allah (peace be upon him) praying in such a state that a sound was coming from his chest like the boiling and bubbling of a cooking pot.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الأفعال المباحة فى الصلاة / 900