I'm installing a new dimmer switch and when I removed the old on/off switch, I found 3 white cables all tied together and 3 black cables. I know that the cables also connected to the light switch in the guest room. I just don't know what to do with my 2 black wires from my new dimmer switch, and the cables in the box. Thanks

Connect the two blacks to the two wires that were on the old switch. DO NOT open any splices that exist in the box.

Worked like a charm! But now I'm hearing some buzzing. It increases as the level of lighting is lowered. Did I miss something? Thanks stanfortyman!