weird idle and ticking noise

[yarddog82]

hey yall! new to the forum and glad to see so much useful information here i have a 97 f350, srw, auto, bone stock, 264k miles that ive had for about a month. the truck runs like a top but when i let the truck idle for a little while the rpm will randomly drop a little then come right back up where it should be. if i blip the loud petal itll idle nice and even again for a good while then itll start doing the same thing. also when im cruising down the road i can hear a slight but steady ticking sound underneath the normal diesel clatter. when the truck is idling in in park the tick goes away, but if i hold the rpm at say 1200 the ticking comes and goes randomly and the rpm will vary slightly as the ticking sound comes and goes. no check engine lights, no oil leaks whatsoever, new fuel filter, starts right up (even tho i dont think the glow plugs are cycling long enough, itll burp a little grey/blue smoke when cold), runs like it should, and seems to have decent power. i saw a similar thread on this forum here - 96 7.3 idles rough at times and "shuts down hard" but i dont wanna hijack someones thread. where do yall think i should start looking, 'cause i definitely dont wanna just throw parts on a truck that otherwise runs great w/o a little diagnostic help