Playing through one of the early levels, the one where you have to head North on the FD highway to meet Gould. After the tremor and you take out the troops in the dust cloud the you reach the check point, I went up to the left where the ammo and grenades crates are, put on nano cloack and sleath killed a troop then paused the game (still cloaked) to go do something. When I un -paused the game there was a constant gun fire noise but nobody was shooting at me, I know this because I have the upgrade that shows where gun fire is coming from.
This fixed its self after I died trying to take the tank on lol, but shouldn't be happening.
cheers carnage