ok there is a huge topic on this at cb7tuner.com, almost every aftermarket flex pipe makes that noise. i had mine replaced, by a profressional all welded and tested for leaks. it made that sound, i drove it back in had another one put on, still the same noise, went on cb7 and there are probably 120 posts from people who had the flex pipe replaced and made that noise.

if you want to get rid of the noise get an OEM flex pipe and have it welded on. thats the only solution i have came across in my search.