It leaks after few minutes of shower turned on. We did some tests and ruled out the shower tile walls and the shower pan. So my guess is that it's the shower feed line pipes, valves, etc. Any suggestions to what to do next? Any other tests I can run?

The tests that so far:
Fill the shower pan using water source other than shower - No leak
Plug the shower drain and fill it with water from other source to see if pan leaks - No leak
Cover shower walls and run the shower - Leaks
Run the shower and divert the water out of the shower - Leaks

More info on the shower might be helpful in answering my question:

Shower has 2 tiled walls and 2 glass walls (including door). The tub is separate. Grouting looks fine. Applied silicone recently to seal any possibility of leaking through the walls.

Doesn't leak when tub water is turned on.

Thanks!

It leaks after few minutes of shower turned on. We did some tests and ruled out the shower tile walls and the shower pan. So my guess is that it's the shower feed line pipes, valves, etc.
I disagree! If you had a pressure leak it would be raining from the ceiling 24/7. You have a drainage leak. Tell me exactly you tested the shower walls and the pan.
You could remover a patch of the ceiling and track the leak back to the source. Let me know what you find. Good luck Tom

I covered the shower walls with plastic (taped some plastic curtains), ran the shower and it leaked after few minutes. For the shower pan, I plugged the drain and let water sit in the pan for an hour, no leak. Then I pour water directly into the drain using buckets (not using shower) without letting it touch the shower pan, no leak.

The reason I think it is the water supply because it leaked when I ran the shower and had the water collected out of the shower without water touching any walls or the pan.

Could it be shower head? Earlier this year we replaced the regular shower head with a shower filter with a handheld wand - could that be a problem? [URL="http://www.amazon.com/Aquasana-AQ-4105-Shower-Filter-Handheld/dp/B004AQZW3A/ref=pd_cp_hi_2"]

We tried removing a patch from the ceiling but for some reason there is another layer of drywall (or something) above the ceiling and nothing much can be seen.

Hope this info helps. Thanks!

The reason I think it is the water supply because it leaked when I ran the shower and had the water collected out of the shower without water touching any walls or the pan.
Ahh! It all becomes clearer now. While not a pressure leak it certainly takes it out of the drainage section. Remove the handle and faceplate and run the shower. Is the water coming down from above or out of the shower raiser connection on the shower valve? Let me know, Tom