Bike Forums - Diagnose my pedal buzz issue

Got a new frame on warranty replacement. Came with press fit BB30 adapters which didn't fit properly - there was some play in the BB.

Hammering on the flats I was getting some 'buzz' through the pedals - sort of muted and more on one side than the other. I went back to the LBS and got them to replace the press fit adapter with the FSA 'sleeve'. This eliminated the play and seems much more solid, but the 'buzz' remains (if not quite as noticeable).

Here's what I know about the problem:

- Only in the big ring
- Only when putting down >400W
- Only when seated
- Seems more pronounced when I am going faster. Downshifting on a slight downhill while pedaling hard always makes it happen. Downshifting on a flat sometimes makes it happen.
- Happens more right after downshifts. Makes sense because that's when my power spikes a bit. If I'm rolling on the flats and I downshift, it will happen for a second or so and then go away.
- More noticeable on the right side, when the pedal is nearing the bottom of the stroke.
- No noticeable sound
- I don't notice it as much on rough roads. Obvious as it's a vibration and on a rough road *everything* is vibrating whereas on a smooth road it stands out more.

I've checked my rear skewer. I suspect my big chainring may be *slightly* bent but this was the case before the new frame and I never got this buzzing issue before.

I have a new chain (ultegra 6700) which replaced an old 6600 chain. The chainrings are 6600 SL and the cassette is 105 and probably nearing the end of its life.

My suspicion is that it could be some sort of incompatibility between the 6700 chain and the old chainrings/cassette. Does this make sense?

Any other possible causes?