veerry interesting(while peering through a tall leafy plant)..... sooo let me get this straight, it only "ticks" while driving...not parked?.. and, the noise is coming through the exhaust?? sure you dont have a header gasket leaking??.. or some exhaust issue, like a donut gasket(if its original exhaust manifolds)... or maybe a collector gasket if it is headers?... possibly the flexplate is hitting something while under driving conditions?... might check to make sure your starter is tight??... hehe, the trouble with ticks.. or was that tribbles?  ticks are hard to trace down.. even harder when it doesnt tick while sitting in the driveway to find it....

I'd have to agree with Jim.  I would start looking at the exhaust system first.

Most times with exhaust leaks, I've heard it at the location of the leak. I've had header gaskets go and it usually is a lot louder than a ticking noise and it came from the engine bay....

LukesVette2007-10-07 05:06:28

My only inclination in the exhaust would be if you still have the converter. On my 76 it is on the right side and when the heat sheild decided it didn't want to be there anymore it began to vibrate at a given RPM which drove me nutz (sorry Scott). Like you I couldn't find it underneath at idle. After some careful inspection i found that it had come loose on the top side (hidden from sight but not feel).

Like Paul within the motor I would tend to look at the lifters or rockers they float with the RPM so it is likely that they can "tick" at a given RPM or under stress. But I would think you should be able replicate the RPM in a garage and identify this. That is what leads me to belive it is more of a motion vibration rather than something attributed to engine revolutions.

(Oh where OH where has our Jethro gone.... Oh where Oh where can he be?)

Calling Dr Adams....
Calling Dr Styer....
Please come to the engine room STAT....    

I have also been leaning towards it being a motion thing Tux, since it can't be duplicated in the garage. Hhhmm, didn't take note of the type road we were on when hearing the ticking. Could have been on some rougher sections, will have to pay attention to that. The convertor is still there so I'll check that out.

Tux, I'll add that to the list. Like Jim said, these ticks are hard to find especially when they can't be duplicated in the garage.

I'm gonna throw this out, and see what ya'll think...
It may be sticking valve, or a valve spring that weakened with the overheating condition. The noise you are hearing from the rear of the car may well be an exhaust "pop" when the valve sticks open when it should be closed. It can be an intermittent "ticking" noise, depending on the severity of the malfunction.
I was leaning towards a u-joint, but you say it will do this in neutral while reving the engine, so that eliminated that.
Also, the noise may or may not have anything to do with the overheat situation...it may just be a co-ink-key-dink that it started after that. It could happen...

Tux was on to another idea...the cat. converter, if you still have it. It's possible the converter got overheated, and some of the substrate inside came loose, and it now floating with the breeze, so to speak. This is normally described as a rattle noise, tho, but a small piece could make ticky noise...

Yeah Joel, I jumped to the conclusion that it was a result of the over heating but you may be right that it could be coincedental.