exhaust fan

got a 4x4x6 tent i got a vivosun 6in 440cfm, pretty new maybe 6 months and its mak8ng a noise i think the bearing are fucked. looking into getting a new one but keep the filter and been looking at few with lower cfm, i feel like it blows hard and will get negative pressure. i have one reagular fan, and two small clip ons.i usually have the vents at the bottom open but closed one since i have another small one going and when the big one is off the other is on. i check it alot since i got clones and would like to avoid lights coming in since i think that may have been my issue on last grow. well when i have the openings closed i get negative pressure even at low it sucks alot. so i was thinking of getting a 6in but lower power? alot of them i find are 350 and up cfm any suggestions or do i need to add a intake fan? i still need a new exhaust fan so can anyone suggest a decent priced one?

Not the quietest in the world, but built like a tank...