Intermittent noises on a bike are the worst thing that can happen to anyone, and it's driving me crazy!
I bought a trekking/city bike a couple of months ago which I use for commuting to work which is around 10 miles both ways. Almost a week after I purchased the bike, I started to feel a "clunk" from what seemed to be the bottom bearings which started to get slightly worse. I took the bike to a LBS which took the B/B out, re-lubed it and the noise went away for a while, although I still slightly "felt" it through the pedals.
I again took the bike to another more reputable shop which double and triple checked everything and told me that the B/B, cranks and pedals are new and in top condition with no play in them.
Tonight I was coming back from work, with a bit more weight in the panniers (work clothes for the week), and after 3/4 on the way back, there was a loud clunking noise coming from the B/B which could also clearly be felt through the pedals.
All through the week when I was commuting to work without the panniers the bike was totally quiet, up to and including this morning.
I'm taking the bike to the LBS tomorrow morning, and would appreciate any input/idea on what this noise could be so I can ask the guy to check it out.