Robocalls are a nuisance that waste your time and often lead to scams. The 'whp' sound mentioned points to automated dialing systems, commonly used by telemarketers or fraudsters to connect you to a live agent or voicemail drop. Hang up immediately upon hearing it—that's smart; it prevents any chance of engagement. Block the number on your phone or through your carrier to stop future calls. If persistent, report to the FCC at fcc.gov/complaints. Enable call screening features on your device for extra protection against unwanted automated outreach.
I immediately hang up when I hear that odd "whp" tone used by automated mailers, so I'm unclear why they keep calling.