You learn something new everyday.
I have been using the Roomba for the past 5 years at least without realizing that the front wheel needed cleaning. I clean the side wheels and the brushes religiously, occasionally using the air compressor, but front wheel, nah.
That's until one of the Roombas started making a funny noise. When it runs, it would sound like it's going over a hump every second. I have heard that before when the bottom brushes are not properly fitted, but this time the problem is not that.
I finally traced it down to the front wheel. I noticed it does have quite a bit of hair stuck in the axle. After struggling on my own for awhile to figure out how to clean the damn thing properly, I turned to YouTube:
Turned out it was pretty easy. You just pull the wheel carrier right off with a bit of force, then pop the wheel off with a flat blade screwdriver. Then I found the culprit:
It's a tiny bead from my daughter's DIY necklace toy set, stuck right between the wheel and the carrier. Problem solved.
Of course, pull all that hair and debris off the front wheel axle makes for much cleaner operation overall. So one more thing to add to the Roomba cleaning checklist!