Maran

I recently cleaned my bearings and cassette myself, and afterwards there is this loud sound when I push hard on my pedals. Could it be the chain? It’s an old Fuji sportif 1.3 with a tiagra shifter. Hope y’all could help.

Maran

Btw it only happens on my smallest cog

Iride01 

Depends on what that loud sound is and when.

Might just be that now that all the sound attenuating gunk has been removed from the cassette and rings that it is now at the normal sound level it should be. Especially if this is in the quiet of your home with your bike in the bike stand and you are just turning the crank with your hand.

The chain does have to bend or articulate around the smaller cog more than the larger cogs. It also can shift position as the cassette rotates and the engaging link and the link that is disengaging do their thing. I'll usually hear and feel a mild rumble after cleaning my cassette and am putting out some power at well over 22 mph and cruising in the 11 or 12 cog.

Welcome to BF.

Rolla

Always look to the last thing you did. Did the bearings get greased and re-assembled correctly? Was the cassette adequately tightened to the freehub?

BikeLite

flatulence

Rogerogeroge

Also depends on what bearings the OP ‘cleaned’ and what was involved ‘cleaning’ them.