Header Leak??

Recently I've been fighting my motor with some odd noises that it makes when its cold. Its a 360 with dougs headers. A little while ago I had a fairly loud "tick tick tick tick" noise coming from one side, this happened after the car sat for a day or so. I thought it was a lifter tick but everything seemed great after I took the valve covers off. I suspected an exhaust leak, so I tightened up the headers and it went away. I took a big screwdriver and put the end on the valve covers and only heard the regular valve-train noise, and I could hear the noise when I placed it on the header pipe.

Now today I started the car up to hear a ticking noise, but not nearly as loud as before, the same kinda noise though. Almost like a ticking with a kinda wooshing noise. I went and tightened the headers bolts and that helped a bit, the noise went completely away after about 5 minutes. I used a Mr Gasket header gasket with some copper RTV on both sides, there is about 600 miles on the motor and I've just recently been having this leak.

What can I do to fix this so I don't have any more leaks? I keep thinking there is something really wrong only to discover a stupid header leak. Should I put in a new gasket? a better one possibly?