hey guys...
i currently have aqua one 2400 external filter, every 3-4 mins it sounds like it builds up alot of air and then i can hear it "whooshing" out all at once,straight out of the horizontal bar into the tank, any ideas why this is happening, it was running dead quite only a few days ago...

sound like air is building in the motorhouse.
This can be caused by turbulence of the rotor.
Check if the tubing on both your inlet and outlet isn't clogged.
I had the same thing happen when I tried to "squeeze" the flow of my canisterfilter by closing one of the valves a lil' bit, when it was still running on my small tank. It resulted in constant air building up and caused my filter to fail performing, cuz it was only pumping air instead of water!

i dont really have a "valve" as such to control flow...they are 2 straight up 1 to 1 and half inch tubes..with no blockage...there are no leaks (air or water) any where in the canister , it just that sounds like its constantly building up and then shoots threw a $hit load of air and water all at once sporadically ...its really annoying, it sounds like the dishwasher ! normally dead silent..

You can try and tilt the running canister to see if any air has gotten trapped.
I usually close the outlet valve for a few seconds and reopen swiftly, but thats gonna be hard to do if you got no valves.
Anyway to refill the motorchamber to check for air?
I got a separate entrance on the top side of the filter to do that.
If that's not helping, I'm out of suggestions....

Dont you just love when stuff fixes itself !!

Im mean seriously, i left it off for around 8 hours, but have a small canister filter running while i was sleeping, woke up, primed it, switched it on, works

I dont know what happened between going to bed and waking up, something fixed it!

Sounds to me like you had some air in the system, and leaving it off has allowed it out, either way im glad it is fixed now