Bubbling chest tubes while on suction

Hello! Today I had a day 3 post CABGs who has had a persistant bubble/ air leak from his MSDT's (chest tubes) and hence the doctors wanted to leave the offending chest tube in. I understand that when assessing for a swing/ bubble I need to stop suction, but this patients bubble was absent when suction was off, and present when suction was on. The nurse who I handed over to said that this is not classified a a bubble, as it was not occuring while he was off suction. My argument was that regardless, a mediastinal chest tube should not be bubbling at all.
What are your thoughts, guys? Would you call this an air leak?
Cheers.