Ah, crud...not only did I hit the ENTER button when I didn't mean to, but I just noticed something ate my cookie.
To continue:
...As Dick said, a jam session is NOT, repeat NOT, a performance venue! If performing solo is the main objective, then find a stage and perform. Jams are for people to participate in the music, and to contribute to the fun and enjoy learning new songs, chords, runs, rhythms, etc. I play a concertina, and there are any number of songs our jam group plays that I do not and would not accompany with the concertina. That's why I take my lap dulcimer along, too. It's quiet, and I can play along with nearly anything "in the background," including behind the guitarist's back, without causing problems for anyone due to my "noise." Perhaps you might suggest to the bodhran and rattle players that they take up a quieter instrument?
But I think Dick's solution of yelling "Take it!" to the bodhran player would work wonderfully! Seems to me it would be a little difficult to keep the song going on only a bodhran, even if the rattler did "chime" in!
P.S. I've been guilty of the rattle thing myself. The first year I attended the Winfield Festival, I wanted so much to be a part of the campground picking that I took my rattle with me from camp to camp, not realizing that it was driving the "bluegrassers" nuts. A kind lady at one of the camps asked if she could use it, and she and her guitarist/singer friend made it abundantly (and politely) clear to me that it was not appropriate to shake the cursed thing to the music they were playing, even if I did manage to keep the rhythms right. I think the singer's comment was something to the effect of "Get that thing away from me--it sounds like a damned rattlesnake!" That was the year I bought my dulcimer. Spent the next year learning some songs to play along next time...
Thanks, lady! And she didn't hurt my feelings, either--in fact thanked me for the use of the rattle and gave me a big grin I couldn't help but return.