I don't think there's anything wrong but the belt is probably glazed and or a little loose. If it's glazed it needs replacing of course, but a lot of guys don't realize the pulleys also need attention. Take a wire brush on an angle grinder and get in the pulley grooves really good and buff the heck out of them. They get glazed over too and sometimes no amount of tightening will make it quit squealing. It's normal for the pump pressure to spike when turned lock to lock. If you get a good new belt on it (Gates not Master Blow) and deglaze the pulleys, I bet it will stop that nonsense.