Engine clicking

I just noticed the other day while my windows were open and I could here the engine better, there was a clicking or ticking noise while cruiusing. When I push the gas in, it goes away. It is an 05 tb ext with the rare v8 w/DOD. It only makes this noise when in 4 cylinder mode. It seems like it is coming from a single cylinder, as it seems to happen 2 or 3 times per second. I actually sounds like a metal rod hitting a metal rod. Please help!

This may be unique to the dod engine, ask your dealer if any info is available pertaining to this.