Rx UART interrupt triggering on PIC24F
That's normal behaviour.  As soon as you enable the receive interrupt it will fire because the Overrun Error flag in the status register will be set.

You will need to clear this error flag in software before you get any more RX interrupts.

See the datasheet for details:
http://ww1.microchip.com/downloads/en/DeviceDoc/39708a.pdf