My new bike feels great, but when I pedal hard I find there is a granite buzz feel only on ht drive side pedal and only on the bottom of the pedal stroke.

Any suggestions what the problem is?

you may have a poor chain line. i would move, and have moved. the cog or the chainring in or out (if you can) a couple of millimeters and see what's what. it's not always easy to see by eyeballing it. or at least that's been my experience.

i just got back from my daily ride, and after swapping cogs yesterday, had the same problem. having experienced it in the past a number of times, it was immediately apparent that i had accidentally changed the chainline. it was an easy fix.

i may also be associated with a flexing crank, chainring or even the frame's bottom bracket shell. often, heavy, or exceptionally strong riders, using somewhat flimsy cranks experience something similar.

Lift the rear the end up and spin the pedals hard. See if you can replicate the sound and get your head a bit closer (try not to wack yourself with a pedal) to pinpoint the exact sound.

It sounds like your chainring screws need to be adjusted...when your chainring isn't perfectly centered, you'll have a high or low spot while pedaling. That high spot will bind the chain a bit and make a slight sound. Hard to tell without hearing it though.

It takes a special wrench to adjust your chainring...I would take it to your local bike shop so they can stick it on a stand/diagnose the issue (and adjust your chainring if that's the case).