Thank you everyone.
I think I've learned more perusing the site recently than in a few years of do it yourselfing.
If it's a pvc pipe hitting a joint or other object, can I just leave it be? While the noise is annoying and perhaps somewhat alarming, so to would be ripping out the drywall, tub, etc. to try to fix it.
Btw, just curious...what is hydraulic jump?