Welcome to the forum.
The lid to the pump is on the vacuum side and is a common source of air leaks. Inspect the gasket and make sure it isn't damaged. If it is, simple job to replace it. Make sure the gasket is clean, then wipe it with a good silicone lube. No harm with excess lube. One suggestion is Jacks, available at any pool store. There are other silicone lubes available too. Don't use vaseline or any petroleum based lube. Try these and see what happens.
Al