jjzepplin, Here is the listing for the solenoid I used.
https://www.ebay.com/itm/123379006152
The bigger can the bigger the volume I think. I experimented with small pieces of metal and plastic for it to hit, and tried coffee cans, dog food cans, etc. It also makes different sounds depending on whether it hits near the edge or the middle of the can bottom, or somewhere in between. Steel seems to sound better than aluminum, to me. It would probably be practical to just rig it up on a bracket and make it hit the dash from somewhere on the bottom or inside. This is a little tiny solenoid, and a bigger beefier one would give you a significant clack. If I decide I want to turn it down, I'll probably switch to one of those little cans that ripe olives or mushrooms come in.
I have heard a lot of things sold as buzzers but they are more of a beeping device and make a high frequency squeal or beep that is pretty much useless for a hard-of-hearing person because high frequencies are often the hardest to hear for somebody loosing their hearing. Those high frequency buzzers, and real buzzers that make a deeper buzzing sound, to me are both annoying. I didn't want to make something annoying, just something noticeable so I can tell the turn signal is on.