Apple has not really changed the notification sounds on the iPhone since iOS 7. So how come you hear strange pings, plunks and doots from your iOS device? No, it is not an app that you have downloaded (although third-party apps may have their own notification sounds). Instead, what you are experiencing is probably the result of updating your iPhone to iOS 13.
The latest iOS update has more than 200 new features, not to mention more than 20 additional changes that iOS 13.1 brings. Among these changes is a new set of sounds for Tapback, an iMessage feature introduced in iOS 10. If you don't know Tapback by name, you know from experience ̵
Tapback notifications used to use the same notification sound as your other messages, and would even arrive silent when in chats. With iOS 13, however, each Tapback has its own unique warning tone. What you hear are the three beeps of someone who "loves" your message, the "boing" of a "question" response, or one of the other four new response alerts. Apple uses these sounds both in chat and throughout iOS, so you can quickly distinguish between a real message and a simple Tapback response.
If you are not a fan of these new sounds, good luck. As it should be, Apple has no way to adjust the warning tones for Tapback, nor does it offer an option to completely mute them. If you don't want to hear a Tapback, you must turn off sounds for all message notifications, which is a bit much if you ask me.
A less radical measure? Just stop your iPhone with the mute switch.