Q: Exhaust leak causing clicking sound.

Yes, this could be the cause, you may have a leak at one of the exhaust manifold tubes. The exhaust manifolds needs to be inspected for a black soot buildup at the joining surface of the cylinder head and exhaust manifold. The exhaust manifold can be restored to possibly cure the leak or the exhaust manifold gasket will have to be replaced. A less likely scenario would be a cracked exhaust manifold tube, upon inspection you will still be looking for a crack with a black soot buildup around the crack. Depending on the exhaust manifold you have installed a cracked tube could possibly be welded. One last possibility may not be an exhaust leak at all but a faulty lifter. A faulty hydraulic roller lifter will not fully pump up and will allow for excessive valve lash causing a click or tap that raises and retreats in frequency and intensity with engine RPM. The use of an engine stethoscope can be used to possible narrow down the affected lifter. Without hearing the noise personally it is hard to say which of these scenarios match you specific issue. You may want to enlist the help of a mechanic, like one from YourMechanic, assist in the diagnosis and repair of this noise.