I have spent a lot of time reading all the BB noise threads I can find (not so easy without the search function) and haven't quite found the answer. I rode my bike, Schwinn Mesa GS (I think it's a '99), in the rain to work the other day. It's got fenders, but no mudflaps. On my ride home, I noticed that there was a click/groan (can sound like a series of clicks on each side) every time either pedal was in the forwardmost position. Here's the strange thing: it isn't there when I'm just spinning to keep up with the wheels, but it goes away when applying a large load such as when I'm really cranking to get up a hill. It's really disturbing because the sound wasn't there before, and after the rain and only a couple hours time it was. Doesn't seem to me to be enough time for rust or any corrosive damage to occur.

What I've done so far:
Tightened the crank retaining bolts
Tightened the chain ring screws
Tightened the seatpost
Greased the chain (with WD-40, I know it's not the best, but I wiped it down well)
Sprayed the BB area with WD-40
Tightened the skewer on the rear wheel
Checked for vibration between the fender and the frame

BTW, there's no side to side play in the BB or crank that I can detect with my hands.

Any ideas?

It sounds like you've corroded/dirtied/otherwise damaged the bearings of the BB. Stock cartridge BBs often have pretty badly sealed bearings, and rain can get into them fairly easily. It's probably nothing serious at this point, since there's no play in the BB. Your options are:

• Replace the BB (this will have to be done eventually)
• Ignore it (it may last for 1000s of miles in the present condition before getting worse)
• Try to force grease into the bearings by spraying a ton of grease in around the spindle of the BB, in the hope that you'll flush out the dirt or corrosion. I haven't used it, but I imagine the spray-can type of white grease would be good for this purpose.

I wouldn't worry about it too much, unless the sound drives you nuts. I have a bottom bracket that makes a noticeable tick whenever I mash too hard on it. I have a replacement waiting for whenever it gets worse, but in more than a year it hasn't changed at all...