Unison cup mute trumpet question

[daerp@mac.com]

I am working a project right at the moment where the trpt section (with cup mutes) is in 4 way harmony for a bit and then ends the phrase with a tapering (dim.) unison. The unison note is the E above middle C and it sounds like there is some distortion or a kind an ack-ack-ack-ack bubbling effect (how descriptive is THAT?):) during the unison. Can anyone help me with this?
Paul

[Markleford]

Do you mean a sound that's like a bad loop in the sample?

- m