Noticed a creek/vibration while pedalling yesterday. Did not notice any loose parts etc. Seemed to come from the drive train (single speed rigid) After a bit I noticed it came every third rotation of the crank. Did place a lot of lube on it last night. Will clean the drive train good tonight. Thinking a stiff link in the chain. What do you think?
Check your chain tension make sure it is not too tight. I get that on my fixed gear whenever I change the tire or rear cog and I get a little over zealous on aligning the rear tire you should have a bit of slack in the chain. If that is good check that your crank arms are tightened to spec if that is good check your bottom bracket might need servicing.