System pressure should be 1-1.5 bar when system is totally cold and should stay below 3 when hot (only top up when cold) if you are too high, bleed a rad until it comes down (may take a while)
This should not be the cause of you issue, i the heating/cooling of rads is random, either you have dodgy thermostatic rad valves, or maybe your system has some air traveling around and all aav's are closed and the air cannot escape (if so you will hear gurgling sometimes at certain rads as the air is on the move) and is dragged around via the pump causing intermittent airlocks.
The other possible cause is a very poor rad balance, easy enough to sort that one.
Possibly suggest get a good service on the boiler and system to identify and hopefully cure the issue