Buzzing and hissing noise when rpm's go up.
 

I hear this buzzing and hissing or whinning sound pretty bad when I take off and when rpm's are hi. It's worse when motor is cold. I thought maybe the exhaust gasket was blown but ppl tel me that it makes a ticking sound if it would be that. It's a 98 f150 4.6 triton. Been a good truck but this has me puzzled... Any ideas?