Who called from 6104953400

Twice this number has called around 830am.  No message is left

Received two calls this morning from this number, 1st time caller didn't leave a message, 2nd time they didn't say anything they just hang up after I said hello twice.
I'm in Oregon

called my cel, left a 'voicemail' of the sound of hanging up. Why do I think they're up to no good?

rec'd a call on my cell and they left a message.  said they are calling from iron mtn customer service.  this is more than likely a wrong number or scam since they called my cell. they are blocked.