I have a shower/tub with a shower diverter you activate by pulling the knob out. Whenever I turn the water on, no problems with the tub part, but When I turned the diverter to shower, the water starts coming out fine for a few seconds,and then the pipes in the wall kind of vibrate and make a weird sound and then the water would pretty much shut off (a small trickle out of the shower).
When I turn the diverter back to tub, the water comes out of the faucet fine. I can get the water to come out of the shower ONLY if I slowly and barely turn the diverter on so that there is water coming out of both the shower and the faucet. If I turn the diverter far enough to almost cut the faucet water off, I hear the noise and the water flow stops. I have bought 2 different fauce/diverters with the same results. And I tried the diverter on another bathroom and it works fine.

And I tried the diverter on another bathroom and it works fine. Are you saying you saying you broke down one shower valve ,removed the diverter and installed it in another shower valve? Please explain farther. What's the name of your valve? How old? Does it blook like this?(see image). Let me know. Tom

Suggest that you remove the shower head and see what happens.

Ok maybe I didn't explain it clearly. I have a bath tub/shower with one on off knob that you turn counter clockwise to turn on the water. The tub faucet has a diverter knob on the front end that you pull out to divert the water to the shower. Originally the issue began as the old diverter broke and when pulled would not stay pulled when you let go of it. So I bought a new 1/2 inch faucet/shower tub diverter and installed it by sliding it on to the exposed 2 1/2 inch portion of copper pipe, then tightening it down with a screw. This worked fine for about 2 weeks.

Now whenever I turn the water on, there is no problems with the tub part, but When I pull the diverter to activate the shower, the water starts coming out fine for a few seconds,then the pipes in the wall kind of vibrate and make a weird sound and then the water from the shower slows to a small trickle though the water valve is fully open, then no matter how tight I have the faucet diverter screwed down, the water forces it off the copper pipe.
But if I push the diverter in and divert the water back to tub, the water comes out of the faucet fine.

I have a second bathroom with the same tub/shower and have taken the new faucet diverter and installed it on that shower and it works fine, so I know the faucet diverter device works.
Does this make better sense?

Sound like the diverter in on the tub spout, where the water comes out for the tub and the shower head is clogged. Try removing the shower head and see if water comes out of pipe for shower.

I removed the shower head and reinstalled the diverter and it works! Yore were correct, thank you for saving me an expensive plumbing bill!