8 weeks old seems incredibly young for a conure. The breeder I got mine from only lets them go after 11 weeks minimum. Makes me think it could be begging for food, was it hand reared or parent reared? The if the beak grinding is accompanied by being all puffy and relaxed it means they're happy and content.
as for Perching on your finger remember at the time of commenting you only had him for 3 days. Imagine his situation, you just got taken from the only place you've ever known with all your friends and family, shoved in a box or small cage put in a car then appeared in a cage with all your friends gone and a big pink giant shoving something in front of your face. I know I'd be terrified of the situation. You need to slow right down and build his trust in you. For some people this can take weeks or even years to do. I can tell you my trick which has worked with 2 green cheeks (can't guarantee it though). Very simply all you need to die is discover a food they like above all I found raisins good for my green cheeks. Then put a pile of them in the palm of your hand held open where your bird's food bowl normally is, then the really hard part. You need to wait and observe. Talk calmly to your bird during this time. Leave your hand for I'd say no more than 30 minutes at a time and replace with the food bowl when your remove your hand. Eventually they will hop onto your hand, when this happens praise them, keep your praise consistent be it either a clicker or I just say "good boy". Keep doing this and they will associate your hand with their favourite treat and will want nothing more than to do what you want. This got my first Green Cheek trained to such a point he would willingly fly to me after 1 week of owning him (unfortunately he died after a month of owning him, myself and the breeder suspect he may have had a heart defect due to the speed he went) with my second he's only just getting the step up and does quite often run away or fly away if he's out of the cage. They all learn at their own pace
