The dashboard sound may be due to clogged AC evaporator drip pan drain. The drain is usually on the firewall on the passenger side. Generally can be cleared with just a finger but might require something else. There might be a YouTube video for your specific car.
A couple of possibilities for water entering the trunk. The rubber seal around the rear deck lid, visually inspect it. It is possible to dislodge a seal, you might be able to reseat it. Any tears or worn spots the seal would need replacement. Seal around rear window may have failed, requiring seal replacement.