Likely two issues at play here. If you’re messing around with the plumbing under the tank, it’s likely that you’re correct, and your plumbing is binding the bulkhead, causing the bulkhead to not seal properly. I’ve done this, and the good news is that it’s a simple fix, just figure out which pipe is causing the stress, and adjust gently till the bulkhead stops leaking (happens on my return line almost every time I pull the return pump out to clean it).
You second issue, the noise, is caused by the lack of a gate valve on your main drain; your pvc can likely flow far more gph than your return, so you use the gate valve to balance the siphon flow and return flow.
I was actually messing around with the plumbing in the overflow. it was very difficult to get my hand in far enough to get a grip and pull out the pipes. I put reducing bushings in the intakes to try and slow the flow down a little. the leak looks like its coming from the main, which was the one i was messing with the most, also the center one and the hardest to get too of course... i turned off the pump last night and drained the overflow box, it should be dry when i get home today. think it will fix itself if i just jiggle on the internal plumbing a bit more?
I'm going to stop by my LFS and pick up a gate valve, & also see what they'll charge me to come out with some brute cans and drain down and refill my tank for me, if they'll do it for 100 bucks or so that's probably worth the piece of mind & i'll probably spend that much buying cans since i don't have any...



