hey i just recently swapped a fresh b16 into my ef, now the engine runs strong and no codes are coming up but when vtec kicks in at about 4500 RPM there is a loud *** rattle coming from the engine?? checked my headers and everything to make sure nothing is loose.. im now stumped can some one help me?

 

My guess is your heat sheild near the cat. Other wise recheck every bolt in the engine bay.