I know you could have fun and convert text into Morse Code on the G Board keyboard, maybe it's some Accesibility setting to help visually impaired people? Samsung even have an App for it called Good Vibes.
https://www.samsung.com/in/microsite/good-vibes/
Could also be the letter Y which is K and T with no gap 
Well all Accessibilty settings are switched off, NFC is switched off as well. And I worked with morse code professionally long long ago, so I know it's a K and a T 
Hehe non professional capacity here, hold a Class A Amateur Radio license, or as we're known here in Ireland, 'Radio Experimenters', sounds like an unusual issue, have no idea what could be sending out K and T at random, i assume it's just those two letters blasting out, at a loss if it's nothing to do with Accessibilities. 
@Jeroen020 , I've seen a few users saying they've been getting weird Morse code sounds recently - and across a range of Galaxy phones (S7, S9, Note10). Some users have identified the Khaleej Times app as being the potential culprit e.g.:
Unsure if it's the same for you.
