creaking handlebar-stem join
Hmm, probably not tight enough or unevenly tight. I wouldn’t use grease – after all, you don’t want the bits to move.
Proper procedure is as follows. Remove bars. Go over the clamp area with a bit of emery cloth removing any burrs or sharp edges on the clamp and stem. Clean both the bars and the stem very thoroughly. You can assemble them dry but if you want to, use some assembly paste – it’s either a sticky grease or grease with grit in it. Then tighten up to the specified torque, or as close as you can get it. Don’t overtighten, but also don’t undertighten. Just firm with an allen key should do it – don’t lean on the thing.