something wrong with my exhaust ....

[valkyrie]

if i just turn on the engine and drive my car, everything is normal ..... but after i drive my car like 70 - 100 mph on the freeway, it starts making a weird noise as if my muffler / exhaust is leaking ........
very annoying noise and in high tone
what is the problem with it
i already have this HKS exhaust for 2 years ........ just now is happening
thanks

[Kit99bar]

are you positive it's your exhaust?

describe the noise better

if it is the exhaust, then it's most likely air leaking out near the flange. Try to tighten the bolts that hold it on