Bottom Bracket Question
 

On a recent ride I was getting a consistent small knocking noise on every turn of my crankset when I was spinning in a seated position. My bike is pretty new (only 300+ miles) and I was wondering if I had a BB issue, so I took it into the LBS the next day. Unfortunately (or fortunately?) the noise wouldn't replicate when they took it for a spin or when the bike was on the trainer at the store. They said they'd get me a new BB, but not so sure that's the problem since we couldn't replicate it. They tightened up the BB a bit and sent me on my way. I have yet to ride it, so not sure if all is okay.

My question is this.... is there any preventative maintenance for the BB? Any lube/grease/product that can be applied to keep things running smooth? Anything that needs to be applied to the pedal spindles for the same reason?

Recommendations?

If I had to guess, since it's a new bike I'd say that the left crankarm might have come a bit loose and tightening it up at the shop should alleviate the problem. Now, that said, a supposed BB creak could come from nearly anywhere on the bike. It could be a saddle that's a bit loose, a stem that's not clamping onto the bars without squeaking, a pedal, damned near anything. As for maintenance with a BB, most nowadays are cartridge units that are sealed and don't let you do a lot, but it depends on which BB you have in the bike. The threads should be greased before it's put in, but a good shop will do that. Pedal spindles should also be greased, but again, a good shop should (operative word there) do this. But all of that greasing is primarily to make sure that the threads don't sieze over time. It often reduces or eliminates noise as well.

This sounds like a saddle/seatpost problem.

You said the noise occurs once per crank stroke, only in the seated position, right? I've had this before and I think what's going on is that the weight on the saddle changes slightly as you pedal. If one of the rails is loose then it will creak.

It's a frustrating problem because you can't replicate it without sitting on the bike...
As for square taper BB maintenance, I like to frequently check the crank bolts for proper torque.