random noise appeared

I just picked up another 97 auto stock but a raptor 100 and told the kdp has been tapped. I've had it for about a month and maybe put 20miles on it and its real sluggish on bottom end till the charger light. But this morning I started it up, let it ideal for 10 mins. All of a sudden a pretty hate full knoise came about. But tap the throttle and it goes away. My question is can converter/ flex plate bolts come lose and make a noise and go away? What about crank bearings? Any help will be awesome thanks