89mustangfive0

try checking your downstream air tube. when i put the h pipe on my car i found that it made a clunking noise at idle and take off.

FivePointOhh

splines are line up correctly. it can only go in one way. i retorqued the bolts and everything looks good. i took it out after that now the sound only happens sometimes. not all the time when i take off. again, it sounds like a vibration. i dont feel it. thats why i dont think its anything in the drive train. something else must be hitting. and i check the downpipe(which i didnt move while cleaning the underside of the car) and nothing is touching. the exhaust is on there tight, i can hardly shake the thing anywhere on the assemblt, its on there tight.

AdderMk2

make sure the driveshaft isnt hitting the floorpan. Exctasy was having the same exact problem.

FivePointOhh

ive located my probelm. the ebrake cable that runs down the driveshaft hump....well right when it makes the first 90* bend the bracket is not actually spot welded anymore. i never noticed before because when i was under the car the cable was always pulled tight so it looked correct but when i went to drive away it was hanging and i would slap against the floor pan (weird!?) anyways, i took it over to a friends this afternoon and threw on two welds and now shes back to normal AND there is an added bonus. my ebrake cable only sometimes would pull tight and i would have to try a couple times before it would actually hold (i always ended up leaving in gear because of this) now the e brake holds all the time. BYAHHHHH