micro bubbles

[clone]

i keep on getting micro bubbles in my main tank, even with the skimmer off.
anyone have any ideas as to why its doing that.
the pump is an external turbo sea 1090.

[Texreefer]

is the pump louder than normal? cavitation is one podssibility. i had the same problem a while back and could not figure it out,, finally found a hairline crack in the bulkhead.. also might try teflon on the threads attached to the intake of the pump