Standalone 

21sp Dahon Espresso. 2 years of hardcore commuting service after buying in used/new condition. Began to make a brrrrp sort of noise and vibration I could feel through the pedals on the "power phase" of my downstroke (rat trap pedals, no clips.) Only under hard acceleration, and as far as I can tell, it's doing it with no difference in sound in every gear. At least in 2 and 3 up front and 3,4 and 5 in the back.

I figured it was most likely a worn chain that was now stretching under load (cheap KMC) and replaced it.

Absolutely no improvement. I would think that if the chainrings were worn. than a new chain would cause at least a different sound and feel running over worn teeth. It is a very cheap looking triple, though.

I have never had any trouble with skipping, and I ride hard over rough urban roads...

When I've had bottom bracket issues before on another bike, the sound was crunchy regardless of the power I was putting in.

So what gives? Is it time for a BB overhaul? Did I screw up the freewheel when I replaced a driveside spoke last week? It did not make the sound after putting the wheel back together.

I don't have the tools or parts to do the BB...

Any ideas?