Making noises on stage just for fun or to represent your concept is a way to get some laughs from the audience.
To get people's attention I use a thing called a "rubber razzer" that makes a funny sound when you blow in one end. Sometimes I use an electronic horn from Radio Shack that plays short segments from 60 different recognizable tunes. In the old days I used a train whistle which always got a chuckle.
Most recently I use a .wav file that I keep on the desktop of my laptop. I tell the audience how I use Internet marketing techniques to bring email orders into my inbox. I've set my Outlook email program to recognize an order and go ka ching, kaching, ka ching, ka ching which, of course, is representative of the cash register ringing. It always gets a laugh.
You can buy sound effect CDs at just about any major computer store, or you can search in any major search engine for sound effects files which you can download and use according to the permission granted by the site.
Think about any of your concepts that could be represented by a sound and you'll have a very easy way to add some humor to your presentation.