Sounds like the gasket may need to be replaced or at least cleaned and oiled. Lime from water can build up there if you have hard water.

I have never heard mine squeal but it does spit and vent for a bit until fully engaged. That's normal. I'd suggest cleaning in and around it well first and apply some vegetable oil to it. That often stops the problem. Also check the pressure regulator/weight vent for blockage and that can get plugged too.

As to reprocessing. Jars and contents have to be hot when they go into the canner or the processing time is voided. So It all has to go back into the pot, be re-heated, re-jarred, new lids, and then fully processed.

Dave