Dimmers that incandescent and LED bulbs have two ratings. The publicized (higher) one is the incandescent rating and the lower rating is the LED rating. It appears that most Lutron dimmers have an LED rating of 150 watts. Here are a few dimmers that have higher LED ratings:

• Lutron Diva DVCL-253P (250 watts)
• Leviton DSL06 (300 watts)
• Leviton DSM10 (450 watts)

...but read the reviews. You never know.

If the LED lamps are actually 11W each, say you do have 25 fixtures, so 25 x 11W = 275W or so total watts, which is well within the capabilities of basic dimmers (basic dimmers usually handle at least 600 watts). If your dimmer is buzzing, it may be old (loose components on the circuit board that are vibrating), it may be an inexpensive dimmer without adequate filter components (which can then cause mechanical buzzing as above), or the dimmer may not be compatible for use with LED power supplies. The buzzing likely does not indicate a safety issue, it's typically just an annoyance. If you want to alleviate the buzzing, replace the existing dimmer with an LED compatible dimmer. The LED bulb manufacturer may have compatible brands/models of dimmers listed to make the selection easier for you.