In order to turn frowns upside down, a mechanic needs to go on a scavenger hunt. Checking off boxes and eliminating options. Be kind and understanding next time your shop guy says he needs some time to fix your creak. Many creaks on a bike sound very similar to a creaking bottom bracket. The entire drive train follows the pattern of 'creak when I pedal and stop when I stop pedaling', unlike wheel issues like brake discs that rub and make a sound whenever the bike is moving.
This one is easy to diagnose: creaks when pedaling seated, then stops when coasting: get up and do your best Mark Cavendish sprint. If the creak disappears when standing, it is time for a seat post cleaning and reinstall of the post and saddle.
Some creaks can be very hard to find, and we have come across new bikes that have suffered from creaking problems which we have failed to resolve through conventional means. In one case it transpired after speaking to the manufacturer that the mitres of the frametubes were misaligned and this was causing the noise!
You really should contemplate investing in a torque wrench too. Overtightening components causes them not to sit correctly up against their neighbouring components which can allow dirt in as well as cause stress riser creaks. Torque wrenches used to be expensive and hard to find in bicycle-relevant torque ranges but this is no longer the case.
How is this helpful? Well, it shows you the anagrams of creaks scrambled in different ways and helps you recognize the set of letters more easily. It will help you the next time these letters, C R E A K S come up in a word scramble game. 2b1af7f3a8