Additionally to what’s been mentioned are you sure he’s not blowing bubbles in his water either? I don’t know the biology behind it but if they’re really thirsty they tend to drink for a minute, then blow blow bubbles loudly. I hear it all the time because I do 60-80 water cups at a time. No idea why, but I’ve seen most species do it 
On another note, I cleaned a couple tubs yesterday where walls were painted at high velocity and that had to make some noise.