DRUMZDUDE

I recently bought a g37 sport and sometimes when the motor is hot(we're talking Phoenix,Az. in the summer), at idle, it makes a strange noise - it sounds lifter like. I consulted the dealer and was told that there is an incompatability issue with aftermarket oil, but not to worry about it. They said that as the viscosity of the oil changes when hot, the engine management system doesn't know what to do as it's calibrated for a proprietary oil that isn't currently available, but not to worry - it's not hurting anything. Also, they said that this engine has a lobeless cam - is that true? Are the valves moved electronically instead of mechanically? Is that how the variable valve timing is possible? Please advise, as the sound makes me worry, not to mention it's embarrassing.