I believe this is the appropriate forum to post this in, as this is a problem specific to fixed gears.

So on my bike, I just bought a new chain. Its a KMC black chain, 1/8. My old chain was a silver 1/8. My chainring and cog are completely the same (Sugino Mighty Comp 52t and phil wood 17t). I adjusted the chain length to be as close as possible to my old chain (although the old chain had a few mm of stretch).

When I put on my new chain, I tensioned the chain it exactly as before, with a noticeable amount of small slack. It is definitely not too tight. However, when I pedal or accelerate in any direction(pulling up, pushing down), the chain makes a terrible noise that is ridiculously loud and sounds like something is scraping. However, when I put my bike on my stand, give one pedal stroke, and let it pedal by itself- it is completely silent. This noise seems to only happen when there is pressure placed onto the drivetrain (accelerating on pedal strokes). I've googled this problem, and it supposedly seems to be a chainline problem. But my chainline was fine with my previous chain that was the exact same size. Whats up with that?

My chainline is the exact same, it seems good enough. The chain is the exact same size and length as the chain before. The tension is not too tight, and has noticeable slack. How did this new problem occur?

New and old drivetrain parts tend to take a while to get to know each other. It'll probably quiet down as it wears in.

You think so? I thought maybe it was this, but the noise is ridiculously loud and I feel the creaks in my feet! Thanks for the advice.

Sometimes things are just noisy. Lube it, ride it, eventually you'll most likely realise either it's quiet or you don't notice it any more. At the end of the day, chains are cheap.

Sorry if I'm repetitive, but- Is it bad if I can actually feel the creaking? Every pedal stroke, I feel as though the chain is rubbing against something terrible, and I can feel the creaks on my pedals. But nothing is creaking. The problem is... I'm actually scared to ride it for a longer distance .

I will lube it and ride it out a bit and update tomorrow. Thanks for the input!

Sounds like your cog is worn. A "stretched" chain accelerates the wear of your other drive train components. A new chain will not interface properly with a worn cog. A new cog will almost certainly solve your problem. From now on, change your chain when 12 links measure 12 1/16", and your drive train will last much longer.

Did you lube your new chain really well before riding? I just replaced BB, cranks and chainring and noticed the same exact noise after leaving the shop. The next day I lubed it up really well and it is super quiet now. Just needed more lube on the chain after putting new parts on.

This was that I was afraid to hear.

My phil wood cog :'(. Thanks. will do.

Yep.. Found the culprit.

Major sharktooth wear on that cog. Your chainring may be badly worn as well.

The chainring seems to be okay, but the cog seems to be terrible now. Will replace asap.

Phil cogs suck. Get an EAI.

Damn, that cog is nassssty.