engine trouble need help please
 

today on my way home from work i was coasting down a hill where i live by going about 60 well i approached the end of the hill and began to put it in to fourth...well the problem is i put it in 2nd on accident and i felt it bog down and it went past 9k which im used to but the fact that i was in 2nd is what worried me. well i caught the mistake before i let off all of the clutch and put it into 4th.

at first i wasn't to worried about it. but i was driving to my gf's house about 15 minutes later and taking off once i got around 5k it started making this weird noise. crackling and like sputtering sorta cant really explain all that good but it gets supper loud and its really starting to worry me.

i checked the oil and it was a little low and added some. probably had NOTHING to do with it but i had to add it anyways lol.

what do you guys think the problem is?

thanks in advance
Joel