did u ever try this? it gives the trumpet a tone almost like it were being played through a crackly speaker. You have to put your lips arount the opening like you were sucking on it, then use the insides of them to buzz.

I tried I made a note come out but it tickled my lips. I saw my band teacher
do it.

I always thought that it was fun to play like that its hard to play with a good tone though