air coming into pool through jets

We have air bubbles coming through the inlet jets. They seem to come in spurts, stopping for a few seconds then another burst of them. It has been doing it since we opened the pool about a month ago. First we lubricated the o-ring on the strainer pot lid, then we replaced the o-ring, we also replaced the o-ring on the automatic clorinator lid. We don't know where else to look. Where are the most common places for an air leak and how do we diagnose the problem?? In case you need to know, its a vinyl in-ground pool with a challenger 1 1/2 hp pump, 9 years old.

air in the system is almost always on the suction side of the pump, so look between skimmer and pump. you can do a leak test, on a calm day, with incense- hold it next to your pipes and move along, look for the smoke sucking into a connection; not the best test method, but it can help!

Your automatic chlorinator whether an in-line type or taps off the pipe, could have a small leak. Check the pressure gage fitting and if you have a bleed fitting check that too.
The drain plug on the pump, the drain plug on the filter, the pump cover should be tight. Everything should be tight but not too tight and the high point should be purged of air.
Can you hear anything like a high pitched sound like a pressure cooker?
It could be a residual air pocket that just needs time to escape.
Lot of guessing here. :)

Do you have a SWCG? How's the water level in the pool - over 1/2 way up the skimmer? Check the skimmer weir to be sure it's not stuck in the closed position.

Do you see air in the pump?