Do it wrong, do it
twice. Do it right,
do it once.
Join Date: Mar 2011
Location: New Zealand
My car ticks due to the incompetence of the company which tried to replace my catalytic convertors and placed a gasket in an inappropriate place. So it sounds to me like a gasket in your exhaust system especially due to the fact it changes frequency when revved. If it sounds like it is coming from your engine it could be one of the gaskets on your exhaust manifold or maybe one of your oxygen sensors has come loose (mine did once).
I could be something else however like tappets but if it gets progressively worse, has or had a burning or exhaust smell you can be sure it is the exhaust system.
All of which has been mentioned above.
(Mechanical Engineer + Mechanic - Alfa)*time = ln(Bad News)