noise

[markwin]

Last week during the playoffs everytime my QB went to call out the signals from the shotgun formation, the visiting team would sound a boating air horn.
It was extremely annoying and disruptive to my signals.
Is this legal?
We are playing in the championship this weekend and wanted to know the answer.
I know natrural made noises are fine but, wanted to clarify this.
Thanks.
Please cite the exact rule if you know it.

HSF rules

Thanks!