Strange sounds from below

[sanuk]

Could be a deviant rock band drummer warming up in the cellar, but this is on my bike and I don't like the sound of it. There's a knocking specifically when starting a ride.  Kind of like a little hammer sound. Never hear it any other time.  Could be the bottom bracket or maybe the rear casset I suspect.  It's irregular and doesn't last long but strangely nearly always after I've either cleaned and/or oiled the chain and rear casset.  Sometimes it seems related to starting out in rain - something I try to avoid - but maybe that's my imagination.  It only lasts about two or three minutes max and only at the start then it peters out and everything's OK.  On a recent long-haul ride I thought it might be caused by overly loaded rear panniers.  But now I got it again back home having just cleaned the bike and re-oiled the chain and starting out with no luggage.  50 yards or less down the road and it stops. I once had a problem before with a loose rear casset, but that doesn't seem to be it. I've had the wheel off.  It looks OK.  Bottom bracket issues would however be a real pain.  Any suggestions, cures?

[BrianW]

Loose rear cassette was my first guess. Sometimes the lock rings will be just loose enough to allow the cassette to rock a bit under load. Are all your spacers there? It could also be a loose BB. Happened to us two weeks ago on our triplet, and was definitely making a clunking noise. Grab your cranks and see if you can move the BB axle at all. Also look to make sure the BB cups are fully threaded in. BBs are not hard to fix, you just need the tool (which is cheap and good to have in your toolbox anyway).

[indyfabz]

I had a periodic knocking last year. Turned out I had a crack in my cassette body cover.

[PeteJack]

"Strange sounds from Below" You might try Beano.

[Miller]

I had something similar and it turned out to be be loose rear skewer. The knocking for me was intermittent throughout each ride. There's a thread somewhere on bike forums about knocking sounds with each pedal revolution. Someone there listed many possible causes.

[etsisk]

I was riding today for the first time after getting a new front derailleur and I kept hearing this rhythmic deep knocking sound. I changed gears, sped up slowed down - the noise basically followed the bike. Great, I thought - I didn't want to take it back to the shop.

Then I looked down and saw my strap-on bottle cage had slid 'round the seat tube and I was hitting it with my pedal. :rolleyes:

[PeteJack]

I had a periodic knocking last year. Turned out I had a crack in my cassette body cover.

Not trying to be smart but just what is a  cassette body cover? I've never heard the term before.

[johnsondasw]

Do you hear it only when pedaling, or also when coasting? I assume it's a pedaling thing. Over the past 60 years or so I've dealt with many knocking/clicking sounds.  The last time, it was more of a clicking one, that seemed to be around only when pedaling under pressure, not under just "maintenance" pedaling.  Of course, it was a slightly loose pedal.  That does not sound like your deal. I have also had the slightly loose rear skewer deal. I once had a much more pronounced knock and it was in the BB.  I had to tighten the lock ring a little more and it fixed the issue. That was on an old 1970s Nishiki.  Great durable bike that died when my son had it in the back  of a pickup, went around a corner too fast and the bike flew onto the pavement. Hmmm, just how fast to you have to turn to throw a bike out of the back of a pickup?