Recently, whenever a person in my Android phone's contact who I have set a customized ringtone sends a Whatsapp text message to me, my phone will play the ringtone as if the person is voice calling me.
This is very annoying and not a Whatsapp "feature" I want. Firstly, it really confused me as I always tought the person is calling me instead of sending Whatsapp message to me. Secondly, the ringtone MP3 is quite long to play. Imagine how frustrating to wait for it to stop everytime it plays just because a new Whatsapp message is received.
Luckily, I found the place to disable this annoyance.
To disable it in Whatsapp, go to Settings > Notifications and untick the checkbox of Contact Ringtone under Message Notifications.
This is another Contact Ringtone for Whatsapp calls which you can see when you scroll down the above screen, and I am OK with that.
If Whatsapp really want to put a feature for customized message tone, they should make use of the SMS tone instead of the call ringtone. I consider this as an annoying bug, and ought to be fixed in their next version release.