I had an annoying squeak / creak coming from the chainstays (some sks longboards). Creaked on every pedal stroke and was worse if I was sat down. I just squeezed the mudguard by hand to give a mm of space either side. Has stayed put and sorted the noise.
(This was after I had removed, regreased, and reinstalled the seatpost, saddle clamp, saddle rail, pedals, crank arms, chainset bolts in search of the offending creak...! Ffs).