This number has called several times before. No response when you pick up. I just let it ring and no voicemail left.

Ditto

Pretty sure it's a telemarketer. Tried calling them back and it's a voice recording saying all agents are busy

Or a scammer.  People online use fake numbers that appear to be local to find identity theft victims.  They call a number and if a person answers that means Their info is likely good.  From there it's very easy to find info related to that number/associated person if they didn't already have it.

Local firefighter just advised our neighborhood that he got a call from this number, trying to solicit money "for local firefighter families".  He also states that the fire houses in the area send their fund-drive information by mail, they do not call and ask for money.  Says do not give them any information over the phone.