Have a 73 with a 75 engine. Every now and then when it was warm out while it was it ldling it I would here a ticking sound that sounds like tapping marbles together. Now that it's getting cold out it s starting to do it non-stop. It's an inconsistent slow clicking noise like i said, sounds like tapping marbles together but in no pattern. Any ideas, i don't know much, trucks starting to run like crap too.