Why would a dimmer start buzzing when some lights are broken?
Dimmers have a minimum rating (as well as a maximum rating) and it is possible that one 35W fitting might not have been sufficient to reach the minimum.

The final lamp breaking might have been a result of the flickering.  Flickering incandescents are not good as it is like they are being turn on and off repeatedly and each time an incandescent lamp is switched on there is an extra rush of current as the filament is not at it's running temperature and therefore has a lower resistance and as a result each time you switch one on it dies a little.  A flickering light is being "switched on" lots of times and dying a little each time.