Could be 1 of 2 things:
1) air in the chamber, but i would think it would be gone after 7 hours,
2) a pinhole, or slightly loose connection somewhere in your intake.
If you took the filter to the sink, overfilled it with aquarium water, then put the top on so that water spills out, reconnect, the bubbles should stop after a minute or so.
Otherwise see #2.
HTH, good luck.
1) air in the chamber, but i would think it would be gone after 7 hours,
2) a pinhole, or slightly loose connection somewhere in your intake.
If you took the filter to the sink, overfilled it with aquarium water, then put the top on so that water spills out, reconnect, the bubbles should stop after a minute or so.
Otherwise see #2.
HTH, good luck.