When you get a tick, squeak or rattle there's the usual things most people to know what to check. But sometimes it's something you haven't heard or thought about and it's maddening.

On one road bike I've had a loud rattling noise driving me crazy and I checked everything, or so I thought. It has rim brake calipers and it turned out to be that aluminum tightening nut on the barrel adjuster. You know, the thing you're supposed to tighten down all the way after you adjust the tension. I did screw it down but not all the way. It was just loose enough to be loud as hell rattling against the caliper.

Another good one is when you have a ticking noise only when you're in the saddle. It can sound like a loose seat post clamp, saddle rail clamp, ext. On two bikes the problem was the seat post was sticking way far down inside the seat tube and at the bottom the post will tick against the inside of the tube. Chopping a couple of inches from the posts cured it.

Any other good ones?

Loose valve stem nut.
Shoelace tip or front derailleur cable crimp tapping the crankarm.

This time of year, I get random buzzing or ticking sounds on the fendered bikes -- from a leaf getting caught in the frame.

this one drove me nuts for about two years.

i have a silca frame pump JIC the CO2 cartridge. gives me no joy.

see that chrome like handle? if it is not seated right then it will make a racket when you hit a bump. but since we seldom use the pump, it stays on the bike thus avoiding detection. when we swapped out the plastic silca pump head for the campy, the game was up for the loose, offending pump handle. and yes, i know i need a new paint job.

I left a threadless stem outside overnight on a garden chair. After I installed it there was a quiet muffled knocking on bumpy roads.
I spent ages checking everything. Eventually narrowed it down to the stem.
A snail had crawled In there and and died. The shell was rattling around the inside the stem.
It actually gave me the crreeps.

I've had a loose spoke hole grommet drive me nuts for a few weeks.
A rear QR skewer on horizontal dropouts that was tight enough to keep the wheel in place, but loose enough to make a creak.

I had a crunchy bottom bracket bearing set the other day - took it out thinking its time to replace, tested it, flawless. Looked inside the bottom bracket shell, and its full of road grit from riding on wet roads, then I see theres a freeken drain hole in there that gives the water tail access from the front tire. Cleaned the bb shell out, cleaned the bb cups as they had collected some of the grit (likely making the noise), gave the threads a bit of grease, and refitted everything - runs like a dream now.
I'll construct a 1 way insulation tape vent for it, so that water can still drain, but theres no way for water off the front tire to get in...