Since last weekend my patrol has begun to make a whistle upwards of 1500rpm (particularly under acceleration) which disappears after about 1-2mins of driving, after of which everything sounds normal again. If I let the car rest for 15-20mins the sound will be back again for another 1-2mins.
From in the cab it sounds like it's coming from the exhaust side or rear of the engine (behind the stereo).
I've already nipped up all of the intake clamps as I initially thought it was boost related.