Hi. My GA16DE 92 makes this Knocking noise once it reaches normal working temperature. I've check the timing and it is ok 10º. I'm using 90 octanes fuel and even when i use 95 octanes fuel, it starts to knock after running for 30 min. When the engine is cold o has not reach the normal operation temperature, it doesn't make any knocking noise. Any idea what the problem could be please?