Frzrbrnt

Hey fellas I have a 04 f150 triton (cam phasers locked) has about 102,000 on it. Since Friday occasionally when I slow down almost to a complete stop I hear one beep like when your door is open and your driving is the best way I can explain it and the oil gauge drops from half way to low for about a quarter second ( which is about the length of the beep) and than shoots right back up to half way it happens more when I'm slowing down to take a turn but it's not always....no stalling no rough take off after I give it gas no rattle I mean it runs like it always has. Any one every experience this before or have any idea?? Not sure if it has anything to do with it but I'm on the east coast and it's been raining it's *** off four days in a row, until today.... idk thanks Semper Fi