I keep my fuel in the trunk of my car and I fly all times of the day and don't experience such problems with my OS engines. My guess is the MAG engine is flawed. Check your low speed needle after 2 or three flights I'm willing to bet it's vibrating very gradually, in or out. My mag .28 did this and it drove me to drink [:@]. Well Ok I already was a drinker [:-] , but it just was a PITA until I put teflon tape around the low speed needle and lowered the nitro down to 5%. GL I'm sure I will be reading more about your engine.