I like to feed with tongs, or you can just pick it up with your hands, either way hold the cricket by the very back legs ensuring your cham can essily hit it. Then just hold it with your arm out straight (makes the cham more comfortable if your body is father away) and hold it in between you and your cham, so that your cham can see you and then prey. How far away from your chameleon depends on his size( id suggest a finger length), a good way to do it is to hold the cricket over the same branch or vine your chameleon is on so that he can move closer. Hold the cricket loosly so the chameleon can grab it and not hurt himself, i like to try to let go right when he grabs it. Youll get the hang of it

Some people also do feeding cups and leave food available 24/7. And others just set a few loose in the cage and leave the chameleon to do his bussiness ( its good to this every now and then because its good for you cham to hunt it.)
But beware about leaving bugs in there, they can actually eat your cham so dont leave alot in all the time. Not to mention bugs might escape depending on your cage.
Hand feeding/tong feeding takes time to work up to sometimes so be patient.
But it also helps to make them for tolerant of you.
As for the rattling, im certain hes just trying to get his tail in the screen so he has something to hold onto. Its common behavior

If youre still worried about it you can post a video, im not sure if you can put videos on here but you can link to youtube

Sorry for the long reply, good luck!
Ps you can let growing chams eat as much as they please, some people even like to split the feeding between two sessions a day. And the rule of thumb is to feed them nothing larger than the part of their forehead between their eyes. (Not the crest).
If you have any questions let me know i have a knack for occasionally not writing clearly

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Best wishes!