I have 2009 Trek 520 with 2,000 miles on it. I just rode 67 miles in Michigan last week and had no problems. I roof racked the bike back to Ohio and on my morning commute this morning, I noticed a creaking-clicking noise. I was able to isolate it to the drive train because the noise goes away when I coast. Also seems related to climbing hills and got worse as the day wore on.

I thought maybe I had a sticky chain link so I degreased and relubricated the chain, same for the rear derailleur and cassette. Noise persists and it's driving me nuts.

Could my BB be going bad after only 2,000 miles? I am a clydesdale and I don't baby the bike on hills. I have already replaced one chain due to stretch around 1,500 miles.

My 520 has external BB bearings. They have no model/part number on them. They are labeled "HD Mountain."

Can anyone tell me how to check this BB? I did give it a spin when I had the chain off and put my ear to the saddle horn. I couldn't hear any grinding or gritty sound.

I tend to fixate on annoying rattles and squeaks so any advice will greatly benefit my sanity.

Just a guess...but a reasonable guess at that: dry or dirty BB threads. Manufacturers don't always adequately lubricate the threads; and some riding conditions can carry fine grit into the threads. Did you ride (or transport the bike) in wet conditions? Removing the BB cups, cleaning the threads and regreasing & reassembling could resolve the issue. Will require a couple tools to remove the crank and BB...and a bit of spare time.

Of course, there are a multitude of sources for strange and undesirable bike noises, and my guess is made partially on your statement that you've eliminated other possible sources outside of the drivetrain. Since you stated you fixate on such things, have you acquainted yourself with Sheldon Brown's writings on such?

If it was/is equipped with a 105 external bb clicks and creaks are a common issue...

My 105 external BB (BB5600) had developed that annoying *click* at ~2k miles of riding in dry conditions. Gave it some love, and it hasn't said another thing in the last 10k+ miles.

My friend's 2006 Trek 520 is in my shop right now for some love... it has that annoying bb click and has a 105 external bb.

Oh yes. I commute daily and the bike gets filthy at times. The Michigan ride was from Petoskey to Wilderness (read: "lots of sand"). Funny, I thought this type of BB was pretty resistant to grit intrusion. I will go pick up requisite tools and give her some PM this evening. I noticed the crank retention screws have a torque spec. How critical is that? I don't own a torque wrench.

Not yet, but I will! Thanks.

From the low mileage on your bike and your riding conditions, the BB threads are a very likely suspect.

The '09 520 was spec'd with Shimano's M453 crankset, and I don't see a tech document for that crankset on Shimano's site. Since it has external BB cups, it probably features the same installation method as Shimano's other external BB cranksets; these have a large "screw" on the outside of the left crank arm which is used to preload the bearing adjustment. It requires an inexpensive tool, and the amount of tightness is very slightly more than finger tight for me. The crank arm is then secured to the spindle with two opposing M6 bolts gradually tightened in turn to 12-14 Nm.

As for needing a torque wrench for this, that's debatable and dependent on your mechanical inclination and how good of a feel you have. FWIW, it's about 10lbs leverage using a foot long wrench. If it's not tight enough and eventually loses it's grip, I imagine it could damage or destroy the crank/spindle splined interface. The Shimano external BB cups I've had are tightened to 35-50 Nm, which is quite tight. If you think you'll have a need for them or be more comfortable using them, you can purchase beam-type torque wrenches quite reasonably at Sears and elsewhere.

Does it do it standing and sitting?

Drop the chain off the crank, and see if the BB feels rough, on its own,

at highway speeds on the roof rack You could have blown grit on the bike into the bearings of the external BB.

Thanks to all who responded. I cleaned out everything, regreased the bearings, and used teflon tape when reseating the bearing cups. The bike is silky smooth again and not a trace of a creak or click.

Here's some info on chain life. 1500 miles is not enough.
https://www.sheldonbrown.com/brandt/chain-care.html
The seals on the bearings are just dust seals.