I6's are known for lifter issues as they age. How many miles are on your ZJ? Usually around 80,000 miles or so the "tick-tick" sound appears and is mostly harmless, My guess is at idle the noise is faint because you're not pushing the engine to create the tick, and at normal driving speeds (55+) the ticking is still there but as your driving along extranious noises (road/tire noise, radio, exhaust, etc.) will contribute to masking out the sound.
You might want to check around your exhaust manifold (or if you have a header instead) for a gasket leak or possible hairline crack. If that's the case it will be a real ordeal to fix, getting to the manifold/header on I-6's at least to me are hard to get to, time-consuming and possibly expensive if you have a mechanic do it so you may want to try to tackle it yourself or seek out a gearhead friend for a favor.
As far as your CC goes, mine does that as well. Do you have a modded exhaust setup or are you running stock? High-Flow CC's will run a bit hotter and a hi-perf. exhaust (i.e. Flowmaster) will definitely heat up more than stock.
Hope this helps,
1998 ZJ 5.9 Limited
1998 ZJ 4.0 Laredo
1995 XJ 4.0 UpCountry