first of all a very warm welcome to u olges , now as far as your questions goes we will try to answer them but remember we are not experts here so ultimately we only answer with our experiences .
1) all efi starts on petrol than switch to cng after few minutes theres no specific time to change over it just change after few kms and yes it can start directly on cng but for that u need a specific settings from cng guys better dont do it and leave it the way company set it .
2) autochoke comes in action when your engine is dead cold and it starts immediately as u start your car and as soon your engine gets it normal your car gets normal rpm .
3) for noise u need to check the source and let us know , it can be check like open your bonnet and start your car and see if u can see the noise comming from any where specific , check all the motors , check your engine mounts aswell , but no one can give u a specific answer unless u give us the source .
4) theres no rocket science of tunning , i take my car for tunning when i feel it needs tunning , for the safe side u need tunning every after 5000km , make sure u topping up your engine oil , air filter is clean , coolant or water level is up to the standard and u are good .
hope this help rest i will leave , kamran , scorpion80, zank , usman and others to give there expert opinions !!
